Honors Algebra 2 question that includes function notation, evaluating functions

Answer 1

If f(x) = x^2 +x

evaluate it at x=3 by replacing x by 3

f(3) =(3)^2 +3 = 9+3 =12

that's all there is to it.

replace x by whatever value you're given into whatever function you're given

if f(x) = (x-3)/(x^2+9)

evaluate it at, for example at x=2 then

f(2) = (2-3)/(x^2 +9) =-1/(4+9) =-1/13

if you get a zero result for the denominator the function is undefined, division by zero is not allowed.