Question

Find the exact value of cos(-7pi/4 radians)

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

Answer 1

@jim_thompson5910 @mathstudent55 @Hero

Answer 2

\[\cos \alpha is periodic with 2 pi\]
\[\cos (-7\pi/4)=\cos \left( \frac{ -7\pi }{ 4}+2\pi \right) =\cos \frac{ \pi }{4 }=\frac{ 1 }{ \sqrt{2} } \]

Answer 3

\[\frac{ 1 }{\sqrt{2} }=\frac{ \sqrt{2} }{ 2 }\]

Answer 4

Sweet, thanks!