# Trig Identity

## Homework Statement

cos^2x - cos^4x = cos^2x sin^2x

N/A

## The Attempt at a Solution

L.S. = cos^2x -(cos^2x)(cos^2x)
= cos^2x -cos^2x(cos^2x)

I'm stuck here. Am I doing something wrong during the first step? Thanks for your help.

What are you trying to solve for, x? Or are you trying to simplify it?

It's trig identity. Trying to make the left side look like the right side.

manipulate the right side, it's easier ... you want it all in terms of cosine

HallsofIvy
Homework Helper

## Homework Statement

cos^2x - cos^4x = cos^2x sin^2x

N/A

## The Attempt at a Solution

L.S. = cos^2x -(cos^2x)(cos^2x)
= cos^2x -cos^2x(cos^2x)

I'm stuck here. Am I doing something wrong during the first step? Thanks for your help.
Didn't we just do one like this? cos^2(x)- cos^4(x)= cos^2(x)- cos^2(x) cos^(x)= cos^2(x)(1- cos^2(x)). Does that help?

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Didn't we just do one like this? cos^2(x)- cos^4(x)= cos^2(x)- cos^2(x) cos^(x)= cos^2(x)(1- cos^2(x)). Does that help?
Sort of but it's too cluttered.

If I try to manipulate the right side, I get this:

= (cos^2x)(sin^2x)
= (cos^2x)(1-cos^2x)

After that, I don't know how to make the cos^4 on the left side.

= (cos^2x)(sin^2x)
= (cos^2x)(1-cos^2x)
foil ...

foil ...
God... how did I miss that. Thanks a lot.

I'm just really tense. Got a huge test tomorrow and trying to cram it all. A week for stuff in a day isn't a good idea... Thanks again!