Problem:
Solution attempt:
create differentiation schema;
apply differentiation schema;
simplify;
add to both sides;
divide both sides by ;
apply trig identity and simplify;
Answer has been verified, thank you all.
Please do not alter the original question. (See Forum Rule #7 here.) We all do some amount of it, but the amount of editing you have done here makes it hard to see what you did and why all these posts exist. It can get very confusing.
-Dan