Answer:
B.
Step-by-step explanation:
Just did the quiz
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
To find it it is
ax^2+bx+c
if the first term (a) is 1 then c=b/2
b=-1/4
(-1/4)/2=-1/4 times 1/2=-1/8
k=-1/8
Answer: only C and E
Step-by-step explanation: i just took the quiz:)