Question

How do you prove `cos (-x)+cos (pi-x) = cos (pi+x) + cosx`?

Answer 1

Proving equation

Explanation:

Prove the equation by using the trig unit circle.
On the unit circle,
cos (-x) = cos x
`cos (pi - x) = - cos x`
The left side of the equation --> cos x - cos x = 0
On the right side,
`cos (pi - x) = - cos x`
The right side --> - cos x + cos x = 0
That proves the equation.