Express the sum or difference as a product.
-$\cos 4 x + \cos 2 x$
A) $2 \cos 3 x \cos x$
B) $2 \sin 3 x \sin x$
C) $2 \cos 3 x \sin x$
D) $2 \cos 3 x$

Question

Quizplus · Accepted Answer

This can be solved using the cosine sum-to-product identity: $\cos A + \cos B = 2 \cos\left(\frac{A + B}{2}\right) \cos\left(\frac{A - B}{2}\right)$. Applying this to $\cos 4x + \cos 2x$, we get $2 \cos 3x \cos x$.

Express the Sum or Difference as a Product cos⁡4x+cos⁡2x\cos 4 x + \cos 2 xcos4x+cos2x

Express the Sum or Difference as a Product $\cos 4 x + \cos 2 x$