Question 773878
Just substitute the express and do the necessary algebra steps.


{{{f(x+h)=1/(x+h)^2}}}


Use that expression in the expression for the difference quotient.
{{{((1/(x+h)^2)-1/x^2)/h}}}


{{{((1/(x^2+2hx+h^2))-1/x^2)/h}}}


{{{((1*x^2/x^2*(x^2+2hx+h^2))-1*(x^2+2hx+h^2)/(x^2+2hx+h^2)x^2)/h}}}


{{{((x^2-(x^2+2hx+h^2))/(x^2*(x^2+2hx+h^2)))/h}}}


{{{(-2hx-h^2)/(x^2*h*(x^2+2hx+h^2))}}}


{{{highlight((-2x-h)/((x^2+2hx+h^2)x^2))}}}