select the correct answer.
which function is an even function?

C.

Step-by-step explanation:

p(x)=sin(x) is an odd function since sin(-x)=-sin(x).

q(x)=cos(x) is an even function since cos(-x)=cos(x).

r(x)=tan(x) is an odd function since tan(-x)=-tan(x).

s(x)=csc(x) is an odd function since csc(-x)=-csc(x).

So the only contender seems to be C.

Let's check.  To check we have to plug in (-x) in place of (x) and see if we get the same function back since we are looking for an even function.

Replace (x) with (-x):

since cosine is even; that is cos(-u)=cos(u) where u in this case is .

So f is even.