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anonymous

  • one year ago

express sin 60 - sin 20 as a product Any ideas of how to start it? lol

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  1. welshfella
    • one year ago
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    there are some identities for sums and differences of sines and cosines as products they;ll be up on the web. i think sin A - sin B = 2 sin(A+B) cos(A- B) ---- ----- 2 2 but i'm not sure

  2. anonymous
    • one year ago
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    I am using a different identity but how would you do it with that identity? @welshfella I am not finding a formula like that either lol

  3. welshfella
    • one year ago
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    http://www.clarku.edu/~djoyce/trig/identities.html

  4. anonymous
    • one year ago
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    @welshfella we havent learned those identities in class however

  5. welshfella
    • one year ago
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    mine was wrong its 2 cos (A+B) sin (a-B) -- -- 2 2

  6. anonymous
    • one year ago
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    @welshfella anything else that would work with it?

  7. welshfella
    • one year ago
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    well i suppose you can do this sin 40 = sin ( 2*20) = 2 sin 20 cos 20 sin 40 - sin 20 = 2 sin 20 cos 20 - sin 20 = sin 20 (2 cos 20 - 1)

  8. welshfella
    • one year ago
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    ohh - im going crazy - its sin 60 !!

  9. anonymous
    • one year ago
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    This question I swear XD This is the formula I think is right to use

  10. anonymous
    • one year ago
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    The second one

  11. welshfella
    • one year ago
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    yes - thats the one i mentioned last

  12. anonymous
    • one year ago
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    So the way you just did it is how its done?

  13. anonymous
    • one year ago
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    Is this right how I did it?

  14. welshfella
    • one year ago
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    yes put A = 60 and B = 20 and simplify 2 cos (60 + 20) sin (60 - 20) ------ ------- 2 2

  15. welshfella
    • one year ago
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    yes you got it

  16. welshfella
    • one year ago
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    2 cos 40 sin 20

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