Question

Use Trigonometric Identities to prove:

Cos(pi - x) = -Cosx

Answer 1

\(\bf cos(\pi - x)\\
cos(a -b) = cos(a)cos(b)+sin(a)sin(b)\\
cos(\pi - x) \implies cos(\pi)cos(x)+sin(\pi)sin(x)\)

what's the cos\((\pi)\) and what's the sin(\(\pi)\) ?

Answer 2

i see cos(pi) = -1 whereas sin(pi)=0
so Ls -1cosx = Rs -1cosx

Answer 3

yes, but 0 * sin(x) = 0, thus, -1cosx

Answer 4

yes i get it now thanks a lot.

Answer 5

yw