# How? Which Trig Identityis that?

How?? Which Trig Identityis that?

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## The Attempt at a Solution

sin^2 = 1- cos^2 ??

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lurflurf
Homework Helper
That looks wrong. It is close to the identity.

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

ehild
Homework Helper
Yes. one of the relevant equation is sin2θ=1-cos2θ.
The other one is cos(2θ)=cos2θ-sin2θ. From these, you get the identity

sin2θ=.5(1-cos(2θ)). Use it.

ehild

Yes. one of the relevant equation is sin2θ=1-cos2θ.
The other one is cos(2θ)=cos2θ-sin2θ. From these, you get the identity

sin2θ=.5(1-cos(2θ)). Use it.

ehild

but there is no sin..

ehild
Homework Helper
but there is no sin..

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

2000sin2(500πt)=1000(1-cos(1000πt)).

ehild

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

2000sin2(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.