- #1

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**How?? Which Trig Identityis that?**

## Homework Statement

[Broken]

## Homework Equations

## The Attempt at a Solution

sin^2 = 1- cos^2 ??

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- Thread starter k31453
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- #1

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[Broken]

sin^2 = 1- cos^2 ??

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- #2

lurflurf

Homework Helper

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That looks wrong. It is close to the identity.

$$2\sin^2(x-\pi/4)=1-\sin(2x)$$

$$2\sin^2(x-\pi/4)=1-\sin(2x)$$

- #3

ehild

Homework Helper

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The other one is cos(2θ)=cos

sin

ehild

- #4

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^{2}θ=1-cos^{2}θ.

The other one is cos(2θ)=cos^{2}θ-sin^{2}θ. From these, you get the identity

sin^{2}θ=.5(1-cos(2θ)). Use it.

ehild

but there is no sin..

- #5

ehild

Homework Helper

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but there is no sin..

The equation you wrote in the first post is wrong. Correctly, it should be:

2000sin

ehild

- #6

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The equation you wrote in the first post is wrong. Correctly, it should be:

2000sin^{2}(500πt)=1000(1-cos(1000πt)).

ehild

Awaks.. IT is solution of the Electrical Engineer : priniciples and application Hambley book.

And they made it wrong. I asked the question though i was wrong.

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