f(x) = x^2 + 3x + 5
f(3+h) = (3+h)^2 + 3(3+h) + 5 ... replace every x with 3+h
f(3+h) = (3+h)(3+h) + 3(3+h) + 5
f(3+h) = (3^2+2*3*h+h^2) + (3*3+3*h) + 5
f(3+h) = (9+6h+h^2) + (9+3h) + 5
f(3+h) = 9+6h+h^2 + 9+3h + 5
f(3+h) = h^2 + (6h+3h) + (9+9+5)
f(3+h) = h^2+9h+23
