# Thread: Trigonometry Derivation Problem...please help :P

1. ## Trigonometry Derivation Problem...please help :P

Hi, I need help trying figure out this problem: I'm trying to figure out the steps to get from one equation to another

Starting Equation:
Y = X (cos^2Ɵ) (cos^2(π/2 - Ɵ)

**missing steps**

Final Equation:
Y = (X/4) sin^2(2Ɵ)

If anyone can help I'd greatly appreciate it. Thanks!

2. ## Re: Trigonometry Derivation Problem...please help :P

You need to make use of the fact that \displaystyle \begin{align*} \cos{\left( \frac{\pi}{2} - \theta \right)} \equiv \sin{(\theta)} \end{align*} and \displaystyle \begin{align*} \sin{(2\theta)} \equiv 2\sin{(\theta)}\cos{(\theta)} \end{align*}.

3. ## Re: Trigonometry Derivation Problem...please help :P

Thanks, but what I really find what's throwing me off is the fact that both the cos are squared in the equation :S

4. ## Re: Trigonometry Derivation Problem...please help :P

It helps to remember that the product of squares is equal to the square of products...

5. ## Re: Trigonometry Derivation Problem...please help :P

I'm trying to use the "power reducing" trig identities on this website, but I'm still not getting it...this is driving me crazy
Table of Trigonometric Identities

6. ## Re: Trigonometry Derivation Problem...please help :P

You are making life difficult on yourself. The only identities you need to use are the ones I gave you. The rest is algebra.

7. ## Re: Trigonometry Derivation Problem...please help :P

Prove It has rightly guided you. However you may look at attached file for solution

8. ## Re: Trigonometry Derivation Problem...please help :P

Originally Posted by ibdutt
Prove It has rightly guided you. However you may look at attached file for solution
You have a typo, the last line should be x/4, not x/2.