Use the Power-Reducing Formulas
-$\cos ^ { 4 } x$
A) $\frac { 3 + 4 \cos 2 x + \cos 4 x } { 8 }$
B) $\frac { 3 + 2 \cos 2 x + \cos 4 x } { 8 }$
C) $\frac { 3 - 4 \cos 2 x + \cos 4 x } { 8 }$
D) $\frac { 2 - 4 \cos 2 x + \cos 4 x } { 8 }$

Question

Quizplus · Accepted Answer

The correct expression for $\cos^4x$ using power-reducing formulas is $\frac{3 + 4\cos2x + \cos4x}{8}$. This is derived by first using the power-reducing formula for $\cos^2x = \frac{1 + \cos2x}{2}$, and then applying it again within the context of squaring $\cos^2x$ to get to $\cos^4x$.

Use the Power-Reducing Formulas - cos⁡4x\cos ^ { 4 } xcos4x

Use the Power-Reducing Formulas
- $\cos ^ { 4 } x$