How to evaluate this function?

Question

Evaluate the function at the indicated values of the independent variable, Simplify the result.

g(x)=x²-4x a. g(2) b.g(a+b)

Answer 1

g(x) = x^2 -4x

g(2) = 2^2 - 4(2) = 4-8 =-4

g(2) =-4

g(a+b) = (a+b)^2 -4(a+b) = a^2 +2ab +b^2 -4a-4b

g(a+b) = a^2 +2ab + b^2 -4a -4b

but "simplest" form is probably just g(a+b)= (a+b)^2-4(a+b)

or if you prefer

g(a+b) = a^2-4a + 2ab +b^2-4b

complete the squares

=a^2 -4a + 4 +2ab + b^2 -4b + 4 - 8

= (a-2)^2 + 2ab + (b-2)^2 - 8