Michael F.

asked • 01/28/18

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
 
The actual answer is:
 
√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)
 
Please help! Thanks!
-A HS Junior in Trigonometry

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

 

1 Expert Answer

By:

Bobosharif S. answered • 01/28/18

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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