## anonymous 5 years ago how do you verify cos(180 + x) = -cos(x)?

1. watchmath

You may use the formula $$cos(a+b)=\cos a\cos b-\sin a\sin b$$. So $$cos(180+x)=\cos(180)\cos x -\sin(180)\sin x=(-1)\cos x - 0=-\cos x$$

2. anonymous

Thank you