Question 93975
Lets work on the right side of the equation:
{{{(2cot(t)/(1+cot^2(t)))=2cot(t)/csc^2(t)=2cot(t)*sin^2(t)}}}
{{{2cot(t)*sin^2(t)=(2cos(t)/sin(t))*sin^2(t)=2cos(t)*sin(t)}}}
{{{2cos(t)*sin(t)=sin(2t)}}}
Voila! The left side equals the right.
Ed Jones