# What is the answer for question 10) http://postimg.org/image/yzcviz60z/

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### 1 Answer

Find exact answers for:

(a) `cos(105^@)`

`cos(105)=cos(60+45)`

`=cos60cos45-sin60sin45`

`=1/2(sqrt(2)/2)-sqrt(3)/2(sqrt(2)/2)`

`=sqrt(2)/4-sqrt(6)/4`

`=(sqrt(2)-sqrt(6))/4`

(Approximate answer -.2588)

(b) `sin(75^@)`

`sin(75)=sin(45+30)`

`=sin45cos30+sin30cos45`

`=sqrt(2)/2(sqrt(3)/2)+1/2(sqrt(2)/2)`

`=sqrt(6)/4+sqrt(2)/4`

`=(sqrt(6)+sqrt(2))/4`

(Approximately .9659)

(c) `sin(225^@)`

`sin(225)=sin(180+45)`

`=sin180cos45+sin45cos180`

`=0+sqrt(2)/2(-1)`

`=-sqrt(2)/2`

(Approximately -.7071)

** Exact answers are usually in simplified, radical form in one term if possible.**