Homework Help: How? Which Trig Identityis that?

1. Jun 15, 2013

k31453

How?? Which Trig Identityis that?

1. The problem statement, all variables and given/known data
[Broken]

2. Relevant equations

3. The attempt at a solution
sin^2 = 1- cos^2 ??

Last edited by a moderator: May 6, 2017
2. Jun 15, 2013

lurflurf

That looks wrong. It is close to the identity.

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

3. Jun 15, 2013

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

4. Jun 15, 2013

k31453

but there is no sin..

5. Jun 15, 2013

ehild

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

2000sin2(500πt)=1000(1-cos(1000πt)).

ehild

6. Jun 15, 2013

k31453

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.