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anonymous

  • one year ago

Medal and Fan, if someone really good at pre calc could help me :)

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  1. anonymous
    • one year ago
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    derive this identity from the sum and difference formulas for cosine: sin a sin b= (1/2){cos(a-b)-cos(a+n)}

  2. anonymous
    • one year ago
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    Alright here's the thing i got 69/100 on this practice test and my teacher is letting me redo for half a credit per correct answer. can someone help explain this one to me please :)

  3. anonymous
    • one year ago
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    @iGreen could you please take a look at this

  4. anonymous
    • one year ago
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    @Loser66 i can show you my work if that helps?

  5. Loser66
    • one year ago
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    Go ahead

  6. anonymous
    • one year ago
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    alright it might take a second there's a table and in the left hand side there's calculations, and on the right side is the reasoning

  7. anonymous
    • one year ago
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    cos(a-b)-cos(a+b) over 2 reason: To manipulate the right side

  8. Loser66
    • one year ago
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    yup

  9. anonymous
    • one year ago
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    ok then -2 sin (-a+b)+a+b over 2) ^2 (a+a+b-b over 2)

  10. Loser66
    • one year ago
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    nope

  11. anonymous
    • one year ago
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    -cos s+ cost= dsin (stt over 2) sin (s-t over 2)

  12. anonymous
    • one year ago
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    = sin a sin b ^2 reason : simplified

  13. Loser66
    • one year ago
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    \(cos (a-b) = cos a cos b + sina sinb\\cos(a+b) = cosa cos b- sinasinb\\----------------------\\\dfrac{cos(a-b) - cos(a+b)}{2} =\dfrac{ cosacosb+sinasinb-cosacosb +sinasinb}{2}\\=\dfrac{\cancel {2} sinasinb}{\cancel 2}= sinasinb ~~=\text{left hand side}\)

  14. anonymous
    • one year ago
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    So thats for the second part that i had gotten wrong right?

  15. anonymous
    • one year ago
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    the first part was correct so i should keep that right? what about the reasonings?

  16. anonymous
    • one year ago
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    I really appreciate your help by the way :)

  17. Loser66
    • one year ago
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    \[cos (a-b) = cos a cos b + sina sinb ~~~~~(\text{identity})\\cos(a+b) = cosa cos b- sinasinb~~~(\text{identity})\\----------------------\\\dfrac{cos(a-b) - cos(a+b)}{2} \\=\dfrac{ cosacosb+sinasinb-cosacosb +sinasinb}{2}~~(\text{open parentheses}) \\=\dfrac{\cancel {2} sinasinb}{\cancel 2}= sinasinb ~~=\text{left hand side}\]

  18. anonymous
    • one year ago
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    Thank you so much @Loser66, you're such a legend

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