I need some help with some algebra problems please.

Question

I don't under stand how to do that following.

Find and simplify the difference quotient f(x+h) -f(x)/h, h cannot equal 0 for the given function.

1. f(x)=5x^2

2. f(x)x^2+3x+9

Answer 1

The first:
f(x+h)=5(x+h)^2=5x^2+10xh+5h^2

f(x+h)-f(x)= 5x^2+10hx + 5h^2-5x^2=
10hx +5h^2

divided by h

10x + 5h

as the limit of h>>0
10x