Answer:
(A), (B) and (C)
Step-by-step explanation:
(A) The given statement is:
Upon solving, we have
Thus, it is a trigonometric identity.
(B) The given statement is:
Upon solving, we have
Thus, it is a trigonometric identity.
(C) The given statement is:
Upon solving, we have
Thus, it is a trigonometric identity.
(D) The given statement is:
Now, if x=0, then
but
Thus, it is not a trigonometric identity.