Question 842919
{{{x/(x+4) - (x+36)/(x^2-16)=(x(x-4)-x-36)/(x^2-16)}}}

then we can write:

{{{(x^2-5x-36)/(x^2-36)=((x-9)(x+4))/((x-4)(x+4))=(x-9)/(x-4)}}}