kaisan 3 years ago verify: sin(x+y)-sin(x-y)=2cosxsiny

1. malexander

2. lgbasallote

take the left hand side...do you know the formula for sin(x+y) and sin(x-y)?

3. malexander

Its an identity.

4. kaisan

i think so but i'm not sure

5. lgbasallote

sin(x+y) = sinxcosy + sinycosx sin(x-y) = sinxcosy - sinycosx can you do it from here?

6. kaisan

it looks familiar but i can't figure it out. is it one of the cosine identities?

7. lgbasallote

no...you substitute those into your problem sin(x+y) - sin (x-y) = sinxcosy + cosxsiny - (sinxcosy - cosxsiny)

8. kaisan

i'm still confused

9. lgbasallote

with what?

10. kaisan

how to do all of this in general

11. lgbasallote

basically you memorize the identities...

12. lgbasallote

i did not do anything fancy...all i did was substitute identities

13. kaisan

oh ok

14. lgbasallote

so regarding this problem...you're good?

15. kaisan

not really...

16. lgbasallote

sinxcosy + cosxsiny - (sinxcosy - cosxsiny) sinxcosy = cosxsiny - sinxcosy + cosxsiny

17. lgbasallote

that's a + not an =

18. kaisan

i don't understand what you did

19. lgbasallote

i distributed the minus sign

20. kaisan

oh ok i see

21. lgbasallote

so you're good now?

22. kaisan

yes thanks ^^