- #1

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- 0

## Homework Statement

Simplify AND Solve for X

cos2xsinx=1

## Homework Equations

The triples, doubles

## The Attempt at a Solution

cos2xsinx=1

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

(-1x)(sinx)=1

-sinx=1

sinx= -1

?

..

:-/

Help.. :)

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- Thread starter CutiePieYum
- Start date

- #1

- 3

- 0

Simplify AND Solve for X

cos2xsinx=1

The triples, doubles

cos2xsinx=1

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

(-1x)(sinx)=1

-sinx=1

sinx= -1

?

..

:-/

Help.. :)

- #2

Dick

Science Advisor

Homework Helper

- 26,260

- 619

The maximum absolute value of cos(2x) and sin(x) is 1. So the only way you can solve that is if cos(2x)=1 AND sin(x)=1 or cos(2x)=(-1) AND sin(x)=(-1). Is either of those possible? If so which one?

- #3

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- 0

I have no idea may i have another clue

- #4

- 3

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anyone?

- #5

Dick

Science Advisor

Homework Helper

- 26,260

- 619

I have no idea may i have another clue

Graph cos(2x) and sin(x) on [0,2pi]. Or do this cos^2(x)-sin^2(x)=1-2*sin^2(x). So you have (1-2*sin^2(x))*sin(x)=1. If sin(x)=u then you have (1-2*u^2)*u=1. That's a cubic equation for u. Can you find the real root?

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