f(x) = 3x2+5x-2, find [f(x+h)-f(x)]/h
f(x+h) = 3(x+h)2 + 5(x+h) - 2
= 3(x2 + 2xh + h2)+ 5x + 5h -2
= 3x2 + 6xh + 3h2 + 5x + 5h - 2
f(x+h)-f(x) = 3x2 + 6xh + 3h2 + 5x + 5h - 2 - (3x2+5x-2)
= 6xh + 3h2 + 5h
[f(x+h)-f(x)]/h = (6xh + 3h2 + 5h)/h
= h(6x + 3h + 5)/h
= 6x + 3h + 5
