Write the expression as the sine, cosine, or tangent of an angle.
-$\cos 7 x \cos 4 x - \sin 7 x \sin 4 x$
A) $\sin 11 x$
B) $\sin 3 x$
C) $\cos 11 \mathrm { x }$
D) $\cos 3 x$

Question

Quizplus · Accepted Answer

This expression can be simplified using the cosine of a sum identity, which states that $\cos(A + B) = \cos A \cos B - \sin A \sin B$. Applying this to the given expression, it simplifies to $\cos(7x + 4x) = \cos(11x)$.

Write the Expression as the Sine, Cosine, or Tangent of an Angle