Question 949097
The meaning of what you wrote is {{{(t/t+1)^2-(t/t+1)-12=0}}}.



Certainly you wanted (t/(t+1))^2-(t/(t+1))-12=0
which will appear rendered as {{{(t/(t+1))^2-(t/(t+1))-12=0}}}.


Multiply the left  (and right)  sides by {{{(t+1)^2}}} which is the common denominator.  You will have a quadratic equation, which you will simplify into general form or possibly be able to factorize.