Michael F.

# Need Help Solving cos -105 with sum or difference identity

The question is cos -105. I know how to do the process for it but for some reason my answer doesn't have the right negatives.
I am getting:

√2 + (-√6)
--------------
4

√2 - √6
-----------
4

My process is:
cos 120 - 225 = -105
1      √2           √3         √2
- __ * ____   +   ____ * - ____   =

2        2             2            2

√2              √6
___   +   -  ____    =

4                4

√2 + (-√6)
_________
4

I don't know what I'm doing wrong. (Math is my weak point, and I struggle with negatives even more so, so I at least know that)

-A HS Junior in Trigonometry

P.S. the worksheet is from Kuta Software, so my teacher didn't create it.

By:

Tutor
4.4 (32)

Mathematics/Statistics Tutor

Michael F.

Ok! Thanks so much!!
Report

01/28/18

Bobosharif S.

You are welcome.
Report

01/28/18

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