Question 1046044
Last one is more interesting.


{{{(1/(7-(x+h))-1/(7-x))/h}}}


-

{{{(1/(7-x-h)-1/(7-x))/h}}}


{{{((1/(7-x-h))((7-x)/(7-x))-(1/(7-x))((7-x-h)/(7-x-h)))/h}}}


{{{((7-x-(7-x+h))/(x^2-14x+hx+49-7h))/h}}}


{{{(-h/(x^2-14x+hx+49-7h))/h}}}


{{{highlight(-1/(x^2-14x+hx+49-7h))}}}, or any minor variation