posted by Ifi .
find the intervals of increase and decrease of f(x)=3/(x*2+11) -1 ?
My f'(x) is-6x/(x^2+1)^2, after that i didn't know how to proceed next bcus i didn't know how to find x to substitute in the f'(x).
Assuming your f' is correct, f is increasing where f'>0.
Since the denominator is always positive, f is increasing where the numerator is positive: x<0
Similarly for decreasing.