something about odd and even function.?

Question

sin –t = –sin t, and

cos –t = cos t.
sin is an odd function, cosine is an even function
What does this mean? would you explain?

Answer 1

It's just as you have written.

sin is an odd function because it follows the concept of
f(x)=f(-x)
cos is an even function because it follows the concept of
-f(x)=f(-x)
I don't have a clue about their applications, but well I guess it's just a name.

Answer 2

for an even function, like x², f(-x) = f(x). 2² = 4 = (-2)². Even functions are symmetric about the y axis, like a parabola with vertex on the y axis.

for an odd function, like x^3, f(-x) = -f(x). (-2)^3 = -8 = -(2^3). Odd functions are symmetric about the origin.