Question

Evaluate the two trigonometric functions using its period as an aid.

1. cos (9pi/2) = ______

Answer - 0

2. cos (-9pi/2) = ______

Answer - 0

Answer 1

\[\cos \frac{ 9 \pi }{ 2 }=\cos \left( 4 \pi+\frac{ \pi }{ 2 } \right)=\cos \frac{ \pi }{ 2 }=0\]
\[\cos \left( -\theta \right)=\cos\theta\ \]

Answer 2

So are both my answers correct?

Answer 3

yes