Question 368351
Substitute, let {{{u=c/d}}}, {{{u^2=c^2/d^2}}}
{{{(c/d+2)/((c/d)^2-4)=(u+2)/(u^2-4)}}}
{{{(c/d+2)/((c/d)^2-4)=(u+2)/((u+2)(u-2))}}}
{{{(c/d+2)/((c/d)^2-4)=1/(u-2)}}}
{{{(c/d+2)/((c/d)^2-4)=1/(c/d-2)}}}
{{{(c/d+2)/((c/d)^2-4)=highlight(d/(c-2d))}}}