## anonymous one year ago Find the exact value by using a half-angle identity. cosine of negative pi divided by eight

1. LynFran

Do u know the half angle identity for cos ?

2. LynFran

|dw:1438032741712:dw|

3. LynFran

|dw:1438033118311:dw|

4. LynFran

what cos -pi/4 =?

5. LynFran

note cos is an even function so $\frac{ \sqrt{2} }{ 2 }$

6. LynFran

|dw:1438033802885:dw|

7. LynFran

|dw:1438035104743:dw|