Rewrite the expression 10cos^4(x) as an equivalent expression that does not contain the power of trigonometric functions greater than 1.

Question

luigi0210 · Answer

Use the idenitity $\Large cos^2x=\frac{1-cos(2x)}{2}$

luigi0210 · Answer

*+$cos2x$ not -

thomas5267 · Answer

Use \cos for cosine.  It is nicer.

anonymous · Answer

This is the answer I got:$$(5/2)-5\cos2x+(5/2)\cos^22x$$
I know it's wrong. Where did I go wrong?

anonymous · Answer

oooh I see now

anonymous · Answer

nope. I'm still getting a wrong answer

anonymous · Answer

@Luigi0210 @thomas5267

thomas5267 · Answer

Use \frac{a}{b} for $\frac{a}{b}$.
Simplify the $\dfrac{5}{2}\cos^2(2x)$ again using $\cos^2(\theta)=\dfrac{\cos(2\theta)+1}{2}$

anonymous · Answer

I got it! Thank you @thomas5267 and @luigi0210