Using the sum formula, show cos(x+pi)=-cos(x)
Can someone tell me the steps of what to do. I can do the sum formula but isn't it different since it equals -cos(x)?

Question

Using the sum formula, show cos(x+pi)=-cos(x)
Can someone tell me the steps of what to do. I can do the sum formula but isn't it different since it equals -cos(x)?

anonymous · Answer

$$\cos(\alpha +\beta)=\cos(\alpha)\cos(\beta)-\sin(\alpha)\sin(\beta)$$ put $\alpha =x, \beta=\pi$ and your answer will drop right out

anonymous · Answer

So just use the formula. Theres no difference even though it equals -cos(x)? Like i don't do the even/odd test after?

anonymous · Answer

no
make a direct substitution
the formula is the formula

anonymous · Answer

the question says "SHOW $\cos(x+\pi)=-\cos(x)$"
make that sub and you will get that answer

anonymous · Answer

got it. So cos(-x)?

anonymous · Answer

or -cos(x)