Express the sum or difference as a product.
-$\cos 8 x - \cos 4 x$
A) $- 2 \sin 6 x \sin 2 x$
B) $2 \cos 6 x \cos 2 x$
C) $- 2 \cos 6 x \sin 2 x$
D) $2 \cos 2 x$

Question

Quizplus · Accepted Answer

The correct expression is obtained by using the cosine subtraction formula, $\cos A - \cos B = -2 \sin \left(\frac{A + B}{2}\right) \sin \left(\frac{A - B}{2}\right)$, where $A = 8x$ and $B = 4x$.

Express the Sum or Difference as a Product cos⁡8x−cos⁡4x\cos 8 x - \cos 4 xcos8x−cos4x

Express the Sum or Difference as a Product $\cos 8 x - \cos 4 x$