Which of the following are identities? check all that apply. a. cot2x + 1 = csc2x b. tan2x = 1 - sec2x c. sin2x = 1 + cos2x d. sin2x + cos2x = 1

I'll assume those are squares.  We know D is an identity:



Dividing through by



That's A.

Dividing the original through by



Not quite B, wrong sign on tangent.  

C has the wrong sign on cosine squared as well.

Identities: A & D

38+105= 143, 39+104=143, and you will find then adding the numbers on opposite sides, moving inwards yields the answer 138 every time. because of this, you’re going to multiply 138 times the number of pairs, which is 34. therefore, 34*138= 4692(i’m sorry if it’s the wrong numbers, but it’s the right concept)