# Thread: Trigonometric solution of cos x =.37

1. ## Trigonometric solution of cos x =.37

I don't understand what to do. It says use a calculator when necessary.

2. are you from GDUB?

3. no whats that? the answer of the problem is:

plus or minus 1.1918 + 2npi

then n = 0, plus or minus 1, plus or minus 2.....

4. Hey, what I meant by GDUB is Glenbard West High School. Are you from that school? Cause the question you posted is the exact same one I'm working on. Do you have a green precalculus book?
Lol, i just thought it was so weird

5. is there like a waterdrop on the book? if so thats mine lol. I have no idea how to solve this.

6. lol, no water drop. the book is mostly green. the seventh edition one. sorry i'm not much help either. i just got on this chapter too. i posted something right before you, should check it out and see if its similar questions to your book.

7. alright thanks. Mine is the 6th edition haha. You're an edition ahead of me.

8. First, make sure your calculator is in "radian" mode, not degrees. Your calculator has an "inverse" button and a "cosine" button. Press "inverse", "cosine", then enter the number and "return". That will give you the "principal value, between $-\pi$ and $\pi$.

Because cosine is an "even function", cos(x)= cos(-x), the negative of that value is a solution also- that's why they say "plus or minus". And cosine is periodic with period $2\pi$. That's why adding " $2n\pi$" for any integer n also is an answer.