Function and function notation

Question

For the function ², evaluate and simplify. = 

Answer 1

10X +3

(f(x+h)-f(x))/h =

5(x+h)^2 +3(x+h) - 5x^2 - 3x all over h =

5x^2 + 10xh + 5h^2 + 3x + 3h - 5x^2 - 3x all over h =

10xh + 5h^2 + 3h over h =

10x + 3 + 5h. Let h go to zero to get

10x + 3 = f'(x) = the derivative of f(x)