# The PE calculator question!



## Techie_Junkie_PE_LEED_AP (Jan 14, 2008)

For the new members who weren't here when the October examinees were preparing...

What's in your calculator case!?

I've used HP calcs for 20+ years faithfully and loved them. The last one I bought was in about 1990, the mighty HP 48SX. $400 in it's day, it could be programmed as a remote control for your TV and you could zip messages across tables, probably why it's banned now.

Anyway, I haven't kept track of them since the 48SX did it all and I was used to it.... until last year. I was forced to update because of the NCEES approved calc list. So, I scoured the net for an HP33s. After getting stiffed twice, I out one on back order and waited. 'Cause I HAD to have an HP. Surprize!! IT STUNK OUT LOUD!!!! I'll never buy another HP calc. I struggled with it for two weeks before I packed it up and bought TWO Casios plus spare batteries cheaper. And I LIKED IT!!

Seriously, if you're going to use ANY calc for the first time on this exam, buy a few and try them during studying and problem solving. Evaluate them with the attitude that if it ain't a warm fuzzzy feeling, you'll send it packing.

Look back in this section to previous posts and you'll see me complaining about the HP33s adn some others replies.

Here's one: http://engineerboards.com/index.php?showtopic=3440

Good luck!!


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## roadwreck (Jan 14, 2008)

I had always used TI's in the past. For the exam I had the casio and one one of the TI's as a back up. Despite leaning towards the TI initially I ended up liking the casio better. Which ever calculator you do decide on, use it while studying and working problems. There is no sense in studying with your old familiar calculator and going into the test with an unfamiliar one.


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## Guest (Jan 15, 2008)

I am also an avid HP calculator user. I tried to use one of the TI models with algebraic entry during the exam (twice) and really got myself flustered by all of the miskeyed entries and need to go back and re-enter series of calculations.

I finally broke down and purchased an HP-33S for my final exam - best $35 investment for piece of mind IMHO.

JR


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## IlPadrino (Jan 15, 2008)

Have you tried the HP 35S? It's got a lot of the "old" feel of the classic but I'm unhappy the sides aren't straight (can't use it as a straight-edge!). It's a little expensive (about $60) but maybe better than the 33S.


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## meschroder (Jan 15, 2008)

Amazing. I had the same upgrade path as you: 15C to 28S to 48sx. I also have one of the little thermal printers.

While I had the 28S (~1988?) I found an original 35 in a thrift store for $8 that worked. I sold it on ebay in 1998 for $198.

My experience was the same with the 33S. I used it because it was the only RPN calculator on the list and I'm algebraically challenged. I still hate it but I bought two of them so I keep one at the office and one in my briefcase. I still use the 48sx for most of my work. The infinite (almost) stack was one of the features I missed the most while using the 33S.



Techie_Junkie PE said:


> For the new members who weren't here when the October examinees were preparing...
> What's in your calculator case!?
> 
> I've used HP calcs for 20+ years faithfully and loved them. The last one I bought was in about 1990, the mighty HP 48SX. $400 in it's day, it could be programmed as a remote control for your TV and you could zip messages across tables, probably why it's banned now.
> ...


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## Capt Worley PE (Jan 15, 2008)

TI-30 user from way back in 1982 (at least)


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## Wolverine (Jan 15, 2008)

I had my trusty, all-powerful, 1985 TI-36-Solar confiscated at the exam because it wasn't an approved "x" model (TI-36x).

Fortunately, I followed the "Bring two calculators" rule and was able to use my HP33S backup. I just was not as efficient with complex numbers on that though and I swear it cost me points.

RPN: you either love it, or hate it (or mildly dislike it, but try to get used to it)


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## Guest (Jan 15, 2008)

Wolverine said:


> RPN: you either love it, or hate it (or mildly dislike it, but try to get used to it)


I was always told to never trust an engineer would couldn't operate in RPN :true:

JR


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## Capt Worley PE (Jan 15, 2008)

rlyflag:

Professors in college told me RPN was a tool of the devil. :true:


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## Guest (Jan 15, 2008)

^^^ Perhaps that's why I have been called a spawn of satan ??!! :asthanos:

JR


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## Capt Worley PE (Jan 15, 2008)

^^ Could be...makes sense!


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## Johnny (Jan 15, 2008)

I was a TI user in high school (36 sounds about right...can't remember), but switched to the HP48g in college. I loved it then and still use it as my primary now. I decided to buy an HP35s (recently added to the approved list) for the exam. It seems o.k., but it'll take some gettin' used to the limited stack. The 48g beats it hands down.

Johnny


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## Strickland (Jan 15, 2008)

Never used RPN in my life, didn't see an HP calculator till College where I was using a TI-86, then an 89 as my 86 was stolen.

I recently picked up the TI-36X, used it for all of a week until I found it couldn't do complex numbers. So I got the Casio fx-115 something or nother. Still not used to it, even after I took it to work to use. Hopefully ponding out problems with it here soon will get me used to the bloody thing.


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## mudpuppy (Jan 15, 2008)

No RPN for me. I used the Casio MX115MS for the exam, and am quite happy with it. I will probably replace my main calculator (TI85) with it when the TI dies. The only quirky thing I came across with the Casio is it tried to tell me that 1 - 2 = 1. It took me several minutes to figure out that was 1 @ 180 degrees, since it does not display the modulus and argument on the screen at the same time. Not a huge deal, but if you're doing simple arithmetic on it and not thinking about complex numbers, it could throw you off. To be safe I changed to rectangular mode instead of polar mode to avoid this problem.


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## MRDPE (Mar 4, 2008)

Go with the HP!

http://theprofessionalengineer.com/2007/12...ctice-problems/


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## Strickland (Mar 4, 2008)

I got the Casio FX-115ES and have been working with it now for a while and overall like it... much better to beable to do complex numbers. I also have a little TI as back up.

Do I wish I could use my TI-89 or TI-92, why yes yes I do as they does lots of the things that are difficult to do with most two line calculators very easily


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## wilheldp_PE (Mar 4, 2008)

The Casio's ability to handle complex numbers is the greatest thing ever (including sliced bread). I originally bought the TI-whatever, then found out that the Casio handled complex numbers while the TI didn't...that's all the convincing it took.

Plus, I hate RPN, so even if the HP does complex numbers, I wouldn't use it.


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## Techie_Junkie_PE_LEED_AP (Mar 4, 2008)

MRDPE, I saw nothing on your website that would even begin to change my mind. The HP 33s is a peice of junk. My long loyalty to HP couldn't even persuade me to use that over priced paper weight.

I don't know about other disciplines, but I wouldn't want my worst enemy to try using it for Electrical, especially Power Depth!

The Casio has superior complex number handling and is easier to find and half as expensive. For the price of a 33s, you can buy two Casios and two sets of spare batteries. Now, if I could bring my HP 48SX, THAT would be a different story!


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## IlPadrino (Mar 5, 2008)

Techie_Junkie PE said:


> MRDPE, I saw nothing on your website that would even begin to change my mind. The HP 33s is a peice of junk. My long loyalty to HP couldn't even persuade me to use that over priced paper weight.


You should be considering the 35s, not the 33s - it's a bit nicer than the 33 from an ergonomics perspective and has some extra horsepower.


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## Dleg (Mar 5, 2008)

Yeah, I don't know why everyone is still talking about the 33. The 35s does everything the 33 does, but in a more traditional HP style. And NCEES added it to the approved calculator list.

I guess it's more expensive, though.


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## Wolverine (Mar 7, 2008)

What's all this talk about TI-36 series not handling complex numbers? Sure it does.

It's possible that I just got used to handling complex numbers the TI way, so that it now seems natural, and that's why I have no endearing love for the HP33S. Plus my HP batteries just died here before it's second birthday even, while my TI is still running on the same power source from twenty years ago.

Whatever you do, bring two. $35 extra bucks is a small insurance fee against having to wash out because your calculator failed.


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## Dark Knight (Mar 7, 2008)

No matter what calculator do you use, please....please....please, check it against the NCEES list. I am surprised to read about calculator incidents test after test. At this stage there is no excuse for that.


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## wilheldp_PE (Mar 7, 2008)

On the Kaplan Sample Exam, they gave a 9th order polynomial characteristic equation for a control system and asked which one of four choices was not a root. When I looked at the solution in the back, there was no work shown...it just said "use your calculator to find the roots". Neither the Casio, nor the TI, will do roots of more than 2nd order polynomials (at least I couldn't find it). Anybody know of a way to "trick" the calculator into solving huge equations...or at least a shortcut to find all the roots of a large polynomial (including complex roots).


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## benbo (Mar 7, 2008)

wilheldp said:


> On the Kaplan Sample Exam, they gave a 9th order polynomial characteristic equation for a control system and asked which one of four choices was not a root. When I looked at the solution in the back, there was no work shown...it just said "use your calculator to find the roots". Neither the Casio, nor the TI, will do roots of more than 2nd order polynomials (at least I couldn't find it). Anybody know of a way to "trick" the calculator into solving huge equations...or at least a shortcut to find all the roots of a large polynomial (including complex roots).


I doubt a problem like this will appear on the real exam, but who knows. Can your calculator do polynomial division up to the level? I only used the calculator for very simple calculations on the actual exam. I remember this problem from Kaplan, and I think I either just did it by long division, or not at all.


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## wilheldp_PE (Mar 7, 2008)

benbo said:


> I doubt a problem like this will appear on the real exam, but who knows. Can your calculator do polynomial division up to the level? I only used the calculator for very simple calculations on the actual exam. I remember this problem from Kaplan, and I think I either just did it by long division, or not at all.


I just guessed on it (correctly, I think). I was just wondering if I was missing a trick that my calc could do. I looked through the instruction book and found how to factor quadractic equations, but couldn't do any higher order equations.


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## Capt Worley PE (Mar 7, 2008)

Maybe try working backwards with each answer??


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## Guest (Mar 7, 2008)

wilheldp said:


> On the Kaplan Sample Exam, they gave a 9th order polynomial characteristic equation for a control system and asked which one of four choices was not a root. When I looked at the solution in the back, there was no work shown...it just said "use your calculator to find the roots". Neither the Casio, nor the TI, will do roots of more than 2nd order polynomials (at least I couldn't find it).


I am not a EE but I am certainly pretty handy with math. 

I would suspect that if you are given a 'higher' order equation that there should be a 'trick' that would allow you to figure out how to solve it.

Do you mind providing the equation + choices? I will take a look at it for you to see if there is anything 'simple' regarding a simplification for solution.

JR


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## benbo (Mar 7, 2008)

I would like to see it too. I gave my book away.

In general, unless you have a real fancy calculator, I still think the easiest method has got to be to just try dividing the answers into the equation. As soon as something doesn't come out easy you can eliminate it.

Remember, this is an s^^9 problem. And assuming nothing obvious factors out, it has got to be tough. You would think if there was a simple way to do it, they would have mentioned it in the answer.


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## wilheldp_PE (Mar 7, 2008)

1.32 The characteristic equation for a given control system is

P(s) = s9 + 30 s8 + 401 s7 + 3176 s6 + 16696 s5 + 61400 s4 + 160324 s3 + 287344 s2 + 318448 s + 162240

Which of the following is not a root of this plynomial?

a. s = -2

b. s = -5 + j

c. s = -5

d. s = -3 +j2

The description in the solution says "This is the point where that expensive calculator your [sic] purchased pays for itself...Simply insert the coefficients into the machine, and the roots are returned."


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## benbo (Mar 7, 2008)

wilheldp said:


> 1.32 The characteristic equation for a given control system is
> P(s) = s9 + 30 s8 + 401 s7 + 3176 s6 + 16696 s5 + 61400 s4 + 160324 s3 + 287344 s2 + 318448 s + 162240
> 
> Which of the following is not a root of this plynomial?
> ...


Six minutes? I really doubt you're going to see anything like this.

I don't think my dividing method will work fast enough, although plugging in the answers is a tried and true method for multiple choice exams. I would start with the s+2 and s+5 and try to either eliminate or include them. After that I might just guess.

Maybe there is a trick for this.


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## ODB_PE (Mar 7, 2008)

This is where the structural guy who has been lurking on this thread goes "WTF is j?" I assume it's what the rest of us call 'i', eh?

either way, you have my sympathies.


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## Flyer_PE (Mar 7, 2008)

A agree. This is well beyond the level of difficulty I would expect to see on the test. Having said that, my response to this question would be to pick B (or C) and move on to the next one. Maybe revisit if you have time at the end of the test.


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## wilheldp_PE (Mar 7, 2008)

I realize that this is above and beyond the level of difficulty of the actual test, but I was confused (as to how I was supposed to do this with my Casio) and angry (that there was no other methods on how to solve the problem in the Solution section) when I tried to understand how to solve this thing quickly.

The answer, BTW, was c.


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## wilheldp_PE (Mar 7, 2008)

benbo said:


> Six minutes? I really doubt you're going to see anything like this.I don't think my dividing method will work fast enough, although plugging in the answers is a tried and true method for multiple choice exams. I would start with the s+2 and s+5 and try to either eliminate or include them. After that I might just guess.
> 
> Maybe there is a trick for this.


I know I'm going to feel like an idiot when I see a response to this question, but how does the "plugging in" method work? I think I understand that by plugging in the "real" answers, roots will make P(s) = 0. Where that breaks down in my mind is working with the complex answers.


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## benbo (Mar 7, 2008)

wilheldp said:


> I know I'm going to feel like an idiot when I see a response to this question, but how does the "plugging in" method work? I think I understand that by plugging in the "real" answers, roots will make P(s) = 0. Where that breaks down in my mind is working with the complex answers.


No, at least I don't think you're an idiot.

Like I said, I would try the real roots first. Once I got to the complex roots I would probably just guess. Unless you had a calculator that could do that sort of thing.

You would have a 50-50 chance at that point, assuming you didn't find the clinker first.

At least that's what i would do on the exam.

another possiblity is you come back at the end of the exam if you have time, convert one of the complex numbers to polar form, and try to plug it in that way. Will that help? I don't know. Probably better than all those j^8s. Then again, maybe I'm messing this all up. I would just guess between the two.

Maybe somebody else will come up with something better.


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## Guest (Mar 7, 2008)

I agree with the other posters - I wouldn't expect a problem of that level of difficulty on the exam.

However, I would like to point out some relevant principles:

1. The Fundamental Theorem of Algebra tells us that a polynomial of n degree has n roots, some of which can be multiple roots. This means that we know that this polynomial of degree NINE has NINE roots.

2. Descartes' Rule of Signs tells us:


The number of positive roots is either equal to the number of variations in sign or less than that by an even number; and
The number of negative roots is either equal to the number of variations in sign or less than that by an even number.
In other words - look for how many times the sign changes. Then apply the rules above.

For the case of your example,

P(s) = zero sign changes; therefore, there aren't any POSITIVE roots

P(-S) = -s9 + 30 s8 - 401 s7 + 3176 s6 - 16696 s5 + 61400 s4 - 160324 s3 + 287344 s2 - 318448 s + 162240

Note that there are nine sign changes, meaning that there are nine NEGATIVE roots.

3. If a polynomial has *REAL coefficients*, then either all of the roots are real or there are an *even number of non-real complex roots in conjugate pairs*.

Since we are looking for the answer that DOESN'T fit - that means we know we can eliminate answers b. and d. because one of the real numbers doesn't fit. Subsequent analysis (Plug-N-Chug) shows that -2 fits, so the answer for which one not fitting is -5 --&gt; Answer c. is correct.

The important take away message is to understand the algebraic principles that allow you to narrow your choices.

I hope this helps. Let me know if you have any questions.

JR


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## ODB_PE (Mar 7, 2008)

jregieng said:


> I agree with the other posters - I wouldn't expect a problem of that level of difficulty on the exam.
> However, I would like to point out some relevant principles:
> 
> 1. The Fundamental Theorem of Algebra tells us that a polynomial of n degree has n roots, some of which can be multiple roots. This means that we know that this polynomial of degree NINE has NINE roots.
> ...


Look at JR bustin out the Descartes after 5 on Friday! :w00t:

:appl: :appl: :appl: :appl: :appl:


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## benbo (Mar 7, 2008)

Very good!

Of course, very few people, except JR are going to have this stuff memorized. So, in the real world, if you just plugged in the real numbers you would have found the -5 without having to look it up.


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## mudpuppy (Mar 7, 2008)

wilheldp said:


> I realize that this is above and beyond the level of difficulty of the actual test, but I was confused (as to how I was supposed to do this with my Casio) and angry (that there was no other methods on how to solve the problem in the Solution section) when I tried to understand how to solve this thing quickly.


If it makes you feel any better, I know of no way to solve this monster using the Casio calculators. I could do it on my TI-85, but not on one of the approved Casios. I'm not saying it can't be done, I just don't know how if it can. But it's a moot point; you shouldn't need to solve anything nearly this complicated on the exam.


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## Guest (Mar 7, 2008)

ODB_PE said:


> Look at JR bustin out the Descartes after 5 on Friday! :w00t: :appl: :appl: :appl: :appl: :appl:


Thanks ... like I said ... don't be hatin' on my analysis !!! 

I wish I was bustin' more than algebra and my ass to get ready for a family/friend party this weekend on a Friday evening!



benbo said:


> Very good!Of course, very few people, except JR are going to have this stuff memorized. So, in the real world, if you just plugged in the real numbers you would have found the -5 without having to look it up.






mudpuppy said:


> If it makes you feel any better, I know of no way to solve this monster using the Casio calculators. I could do it on my TI-85, but not on one of the approved Casios.


Did you say solution ??

B)

JR


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## wilheldp_PE (Mar 7, 2008)

jregieng said:


> Did you say solution ??
> 
> 
> B)
> ...


Damn...any chance of my convincing the proctor to let me bring in a laptop with MathCAD loaded on it?


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## benbo (Mar 7, 2008)

I still remember JR's elegant dissertation on Monty Hall.


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## jdd18vm (Mar 8, 2008)

jregieng said:


> Thanks ... like I said ... don't be hatin' on my analysis !!!
> I wish I was bustin' more than algebra and my ass to get ready for a family/friend party this weekend on a Friday evening!
> 
> 
> ...


sheesh.....i cant even get partial fraction expansion down, I'd be picking C on this one. kudos!


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## benbo (Mar 8, 2008)

jdd18vm said:


> sheesh.....i cant even get partial fraction expansion down, I'd be picking C on this one. kudos!


A wise pick in this case! I think that's the answer.


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