NCEES Power #115

[mike123]

Anyone know how to enter the below formula work out the area under the curve using the CASIO fx-115MS

Answer = 1/pi * integrate Sin(x) between 45deg and 180deg ?

Answer = 0.543A

 

[Flyer_PE]

I think you are actually asking about question #115.

Not knowing anything about the Casio, I have to ask why you wouldn't just do the integration manually?

The integral of sin x is -cos x

All you need are the value for pi, cos 45o, and cos 180o

cos 180o = -1

cos 45o = 1/sqrt2

It's simple algebra from there.

 

[mike123]

Good spot. The question number indeed should read #115 and not 114. I would fix but I can't figure out how to do it.

Just though I should learn how to use the calculator as a way to double check the answer, and to save a precious minute. Especially if there are a number of integration problem during the exam. The minute saved adds up.

 

[geofs_PE]

First, change to radians: [shift] [Mode] [4]

Then:

∫(sin(X),(π/4), π)

ANS/ π =

The '/' is the 'divided by' operator, I don't seem to have a symbol for it.

The time it takes the calculator to solve the integral is probably ~60 sec. or so, so be patient.

This gives the correct answer but I agree with Flyer, it's faster and easier to do the integration manually.

 

[BamaBino]

If this problem (115) had instead asked for the RMS value of the current, would the correct answer be 0.674 amps?

 

[Flyer_PE]

Good spot. The question number indeed should read #115 and not 114. I would fix but I can't figure out how to do it.

Title updated.

 

[ChrisB]

Coming back to this question, why do they use radians (1/pi) prior to the integral, but then degrees (45 - 180) after the integral sign? The handbook shows everything being in radians (before and after the integral) for the equation. When using radians for the entire equation, I'm getting a different answer than 0.543A. I'm getting 0.00044A.