Cram for PE actual book Sym Comp 3.1.2 problem 1. Help please

I keep getting 91@-15 degrees for Ic and I don't know what I'm doing wrong, I got Ia and Ib correct. 

For Ic I'm doing the following forumula:

Are you getting -15° or -158°, because I'm getting the latter?

Looks like 21° is a typo.

Double checked using online calculator:

Chattaneer PE said:

Are you getting -15° or -158°, because I'm getting the latter?

Looks like 21° is a typo.

Click to expand...

Yeah i was getting -158, just showed -15 on my calculator and i wasn't scrolling over enough because it wasn't saying positive 21 like the book lol. 

@Cram For The PE Do you have a link to the eratta's for all your materials? 

its may be the other way to write -158 is +21

180-158=21

-158° = 202° ≠ 21°

(360 - 158 = 202)

21° is a typo. It should be -158°. This was a misuse with my calculator. As you know, when the resultant lies in the third quadrant your calculator can trick you if you have it set wrong. If i break them all down you see the following:

44.99+53.62j-80-50-86.6j=-85-32.9j

you can see from -85-32.9j that the resultant must lie in the third quadrant. So having it as 21° is not true. It is really 180° out from 21°. If you add the vectors you will see. Below is a to scale drawing of the vectors.



Thank you for bringing this to my attention. I will get it fixed in the next edition.