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)?

Answer 1

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

Answer 2

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

Answer 3

no
make a direct substitution
the formula is the formula

Answer 4

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

Answer 5

got it. So cos(-x)?

Answer 6

or -cos(x)