Step 1: Recall the trigonometric identity.
The cosine addition formula is:
cos(a + b) = cos(a)cos(b) − sin(a)sin(b). Step 2: Substitute the given values.
Here, a = x and b = yx, so
cos(x + yx) = cos(x)cos(yx) − sin(x)sin(yx). Step 3: Final conclusion.
The expression exactly matches option (A).