Solving derivative with roots in denominator

[reggiehaft]

Homework Statement

i have to get f'(x) using the limit definition of the derivative (lim as h approches 0 f(x)= (f(x+h) - f(x)) /h) and I don't know where to start. f(x)= 3/(sqrt(1+x^2)

Homework Equations

what do I do with the (sqrt(1+x^2)


3. The attempt at a solution
I have gotten to lim as h approches 0 f(x)= (f(x+h) - f(x)) /h) = 3-3/ sqrt(1+(x+h)^2- sqrt(1-x^2)/h

 

[Dick]

Uh, it's lim h->0 of (f(x+h)-f(x))/h. Your difference quotient is kind of messed up. Can you fix it up first?

 

[Mark44]

I might add that the numerator won't be 3 - 3 as you show.

3/a - 3/b != (3 - 3)/(stuff in the denominator)

Before you start adding the terms in the numerators of fractions, the denominators have to be the same.