Cos (270+x) is equivalent to:

Cos (270+x) is equivalent to:

A: -Sinx
B: Cos x
C: Sin X
D: -Sin x (I know it is repeated, idk why on my test)

By the cosine addition formula:
cos(A + B) = cos(A)cos(B) - sin(A)sin(B).

With A = 270° and B = x:
cos(270° + x) = cos(270°)cos(x) - sin(270°)sin(x)
= (0)cos(x) - (-1)sin(x)
= sin(x).

Therefore, the answer is (C).

I hope this helps!

cos (a + b) = cos a * cos b - sin a * sin b

Substituting in a = 270 and b = x:
cos 270 * cos x - sin 270 * sin x

cos 270 = 0, causing the cos 270 * cos x to cancel out. sin 270 is -1:
0 - (-1)*sin x
= sin x

The answer's C.

cos (a+b) = ? I am sure you have had this explained before. Now learn it.

C) sin x