Question

Is cos(-x) = cos x? why?
I'm confused.

Answer 1

oh is it because of the graph? symmetrical to the y-axis then sin x is odd because it is symmetrical to the origin?

Answer 2

cos(x) is an even function
f(-x)=f(x) means f is an even function
what even function is that it is symmetrical about the y-axis
this means the graph can be founded about the line that is called the y-axis and see half the graph lay perfectly over the other half

Answer 3

and yes sin(x) is odd
so sin(-x)=-sin(x)

Answer 4

thank you!