Homework Help: Difference quotient question!

1. Sep 10, 2011

nukeman

1. The problem statement, all variables and given/known data

I am having trouble with a couple difference quotient questions. Here is a question I cant seem to solve.

Evaluate the difference quotient for the given funtion and simplify your answer.

f(x) = 4 + 3x - x^2 , f(3 + h) - f(3) / h

2. Relevant equations

3. The attempt at a solution

I have tried it a couple times, and cant seem to get it right!! Any help at all would be great!
Thanks.

2. Sep 10, 2011

Ivan92

Remember the difference quotient is:

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

Since you say that f(x) = 4 + 3x - x^2 plug that in for f(x) in the equation. I don't know why you would plug in f(3).

3. Sep 10, 2011

Ray Vickson

Should we assume you mean [f(3+h) - f(3)]/h, rather than what you wrote (which meant f(3+h) - [f(3)/h])? Anyway, if you meant the first one, what is stopping you from substituting x = 3+h into the formula and simplifying it, then substituting x = 3 and simplifying (or setting h = 0 in your first result)? When you say you can't get it right, how do know your results are wrong? Are you given an answer, and cannot seem to match it?

RGV