Answer:
<em>Observe the attached image</em>
Step-by-step explanation:
A function f(x) is even if

This means that an input value x and -x have the same output value y
Therefore, check the graph and if it has equal values of y for the values of x and -x, then it is an even function.
Then the graph of
will have symmetry with respect to the vertical axis
Observe in the attached image the graph of 
It always has the same values of y for x and -x. Then
It's an even function.
Sure what's your question?
Examples of constant :
2, 5, 0, -3, -7, 2/7, 7/9 etc.
Examples of variable :
The letters x, y, z, a, b, c, m, and n
Step-by-step explanation:
it's explained in the solution