PLEASE help with rational functions assignment

I have this assignment due wednesday.. and I've started it.. but I want to make sure I'm on the right track.. and some of them I have no clue where to start. Anyways.. if anyone can help it would be much appreciated

1. Determine the derivative of

f(x)= __2x^2 - 1__

.............x

from first principles. Use the quotient rule to verify your answer.

2. The graph of

f(x)= __ax + b__

......(x -1)(x-4)

has a horizontal tangent line at (2,-1). Determine the values of a and b.

3. The tangent line to the curve defined by

g(x)= __x^4 - 2x^3 +3__

..............-6x

at x= -1 intersects the curve at two other points **P** and **Q**. Determine the coordinates of **P** and **Q** algebraically. Illustrate this situation with a graph. (*to graph g you need to create a table of values*)

HINT: You need to research L'hopital's rule in order to complete this question

I have no clue what L'hopital's rule is, because we've never learned it, so if someone could also explain that to me.. that would be great.

Thank-you!