## anonymous one year ago What is (cos Θ − cos Θ)^2 + (cos Θ + cos Θ)^2? sin^2 Θ 4cos^2 Θ 8 cos^2 Θ

1. Astrophysics

cos theta - cos theta = ?

2. Astrophysics

it's like saying x - x, what does that give you?

3. anonymous

I know that part equals out to 0, but then I'm left with (cos theta + cos theta)^2

4. anonymous

I can't figure that out :(

5. Astrophysics

6. anonymous

It becomes $\cos ^{2}\theta + \cos ^{2}\theta$

7. zepdrix

Expand? 0_o But you said x-x = 0 why not apply that thinking to the other one? x+x = 2x

8. anonymous

That's why I'm confused, it can't just equal 2x

9. zepdrix

...?

10. zepdrix

The other one is x+x

11. Astrophysics

the (cos theta+ cos theta)^2 term

12. Astrophysics

cos theta + cos theta = 2cos theta, now square it

13. anonymous

Ohhh

14. anonymous

Well then it would be $4\cos^2 \theta$

15. anonymous

Well I'm an idiot

16. anonymous

It was simple... -_-

17. Astrophysics

Lol, don't worry for some reason I was thinking costheta+ sintheta

18. Astrophysics

But in any case if you took long way or just added right away, you'd get same answer

19. anonymous

It's okay, thank you for helping though!

20. Astrophysics

Yw :)