How? Which Trig Identityis that?

[k31453]

How?? Which Trig Identityis that?

Homework Statement

Homework Equations

The Attempt at a Solution

sin^2 = 1- cos^2 ??

 

[lurflurf]

That looks wrong. It is close to the identity.

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

 

[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

 

[k31453]

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]

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

 

[k31453]

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.