Which of the following are trigonometric identities? Check all that apply.

A. sin^2 (x) + cos^2 (x) = 1
B. sec^2 (x) + csc^2 (x) = 1
C. tan^2 (x) - sec^2 (x) = 1
D. sec^2 (x) - tan^2 (x) = 1

Question

Which of the following are trigonometric identities? Check all that apply.

A. sin^2 (x) + cos^2 (x) = 1
B. sec^2 (x) + csc^2 (x) = 1
C. tan^2 (x) - sec^2 (x) = 1
D. sec^2 (x) - tan^2 (x) = 1

anonymous · Answer

I know that D is a  trigonometric identity, however, I am not sure about the rest. Help would be much appreciated.

anonymous · Answer

you gave the answer yourself :D
if the last one is an identity, C cannot be an identity , look at its left hand side , its negativve of L.H.S in D

anonymous · Answer

So A and B are not identities either?

anonymous · Answer

NO THEY ARE
first one is an identity 
now if you take reciprocal of sin^2(x) and cos^2(x), it gives csc^2(x) and sec^2(x).. which provves second

anonymous · Answer

Great! Thank you! So the answers are A,B, and D!