Question

21. Which of the following is an identity? a) sin (a) cos (a) = (1/2) sin(2 a) b) sin a + cos a = 1 c) sin(-a) = sin a d) tan a = cos a / sin a

Answer 1

A

Explanation:

`\sin(2 \alpha ) = 2 \sin( \alpha ) \cos( \alpha )`

`\sin( \alpha ) \cos( \alpha) = (1)/(2) \sin( 2\alpha )`