Cot x sec^4 x=cot x + 2tan x + tan^3 x

Recall the Pythagorean identity:



Divide through by and you get



On the left hand side of your equation, use this expansion for :



and simplify using the fact that . You end up with



so this is an identity and holds for all in an appropriate domain.

There are 48 blue cards total

The answer is e &