A 4th power is the same as squared squared. So ; and
There is an identity that connects csc squared and cot squared:
Once you recognize these two facts, this is a farily simple problem.
1. Rewrite the left side in terms of csc squared:
2. Replace the csc squared's with cot squared plus one:
3. Simplify. I'll leave this part up to you with these hints:
Use FOIL or the pattern to multiply out .
Combine like terms while being careful to notice the minus in front of .
If you do this correctly the left side matches the right side fairly quickly.