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kaisan

  • 3 years ago

verify: sin(x+y)-sin(x-y)=2cosxsiny

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  1. malexander
    • 3 years ago
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    cos(x+y)=cosxacosy-sinxsiny cos(x-y)=cosxcosy+sinxsiny addition produces 2cosxcosy

  2. lgbasallote
    • 3 years ago
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    take the left hand side...do you know the formula for sin(x+y) and sin(x-y)?

  3. malexander
    • 3 years ago
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    Its an identity.

  4. kaisan
    • 3 years ago
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    i think so but i'm not sure

  5. lgbasallote
    • 3 years ago
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    sin(x+y) = sinxcosy + sinycosx sin(x-y) = sinxcosy - sinycosx can you do it from here?

  6. kaisan
    • 3 years ago
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    it looks familiar but i can't figure it out. is it one of the cosine identities?

  7. lgbasallote
    • 3 years ago
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    no...you substitute those into your problem sin(x+y) - sin (x-y) = sinxcosy + cosxsiny - (sinxcosy - cosxsiny)

  8. kaisan
    • 3 years ago
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    i'm still confused

  9. lgbasallote
    • 3 years ago
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    with what?

  10. kaisan
    • 3 years ago
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    how to do all of this in general

  11. lgbasallote
    • 3 years ago
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    basically you memorize the identities...

  12. lgbasallote
    • 3 years ago
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    i did not do anything fancy...all i did was substitute identities

  13. kaisan
    • 3 years ago
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    oh ok

  14. lgbasallote
    • 3 years ago
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    so regarding this problem...you're good?

  15. kaisan
    • 3 years ago
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    not really...

  16. lgbasallote
    • 3 years ago
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    sinxcosy + cosxsiny - (sinxcosy - cosxsiny) sinxcosy = cosxsiny - sinxcosy + cosxsiny

  17. lgbasallote
    • 3 years ago
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    that's a + not an =

  18. kaisan
    • 3 years ago
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    i don't understand what you did

  19. lgbasallote
    • 3 years ago
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    i distributed the minus sign

  20. kaisan
    • 3 years ago
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    oh ok i see

  21. lgbasallote
    • 3 years ago
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    so you're good now?

  22. kaisan
    • 3 years ago
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    yes thanks ^^

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