how to tell that what trigonometric identity (a.k.a. Pythagorean trigonometric identity) will work on the given equation , so then you can simplify the equation accordingly in order to apply that identity?
I'm talking about applying these if you still dont know what i'm saying :
$\sin^2A + \cos^2 A = 1,$
$\tan^2 A + 1 = \sec^2 A,$
$\cot^2 A + 1= \csc^2 A$
Examples would be great, thanks in advance.