Question

How do you prove sin(180°+a) = -sin(a)?

Answer 1

`:. sin(180^0+a)=-sina.`

Explanation:

We expand `sin(180^0+a)` using the formula `sin(A+B)=sinAcosB+cosAsinB`

`:. sin (180^0+a)=sin180^0cosa+cos180^0sina`

In this, `180^0=0, cos180^0=-1`

`:. sin(180^0+a)=-sina.`