Question

Which of the following are identities? A) sin^2x - cos^2x = 1 . B) sin^2x = 1 - cos^2x . C) tan^2x = 1 + sec^2x . D) cot^2x = csc^2x - 1

Answer 1

B ) sin² x = 1 - cos² x
sin² x + cos² x = 1  ( correct )
D ) cot² x =  csc² x - 1
cos²x / sin²x = 1/sin²x - 1 = (1-sin²x) / sin²x = cos²x/sin²x
Identities are B ) and D).