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mathslover

sin ( 90 + theta ) = cos theta prove^

  • one year ago
  • one year ago

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  1. satellite73
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    i guess it depends on what you can use if you can use the addition angle formula, that would work if not maybe with a triangle you can see it

    • one year ago
  2. mathslover
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    i want to do with the triangle one but m wondering how will you show (90+theta) in a right angled triangle?

    • one year ago
  3. satellite73
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    |dw:1350098235823:dw|

    • one year ago
  4. mathslover
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    yes but that is 90 - theta? do 90-theta has any relation with 90 + theta ?

    • one year ago
  5. satellite73
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    \[\cos(x)=\frac{a}{c}=\sin(90-x)=-\sin(x-90)\] \[=\sin(x-90+180)=\sin(x+90)\]

    • one year ago
  6. mathslover
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    how : -sin(x-90) = sin(x-90+180) ?

    • one year ago
  7. satellite73
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    third equal sign because sine is odd, fourth because \(\sin(x)=-\sin(x+180)\)

    • one year ago
  8. mathslover
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    Gotcha now, thanks a lot!

    • one year ago
  9. satellite73
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    your on the other side of the unit circle |dw:1350098472701:dw|

    • one year ago
  10. satellite73
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    yw

    • one year ago
  11. mathslover
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    hey, how you did this step? : \[\large{-\sin(x-90) = sin(x-90+180) }\] ?

    • one year ago
  12. mathslover
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    @satellite73 did you subtract sin(180) both sides?

    • one year ago
  13. satellite73
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    i added 180 inside because \(\sin(x)=-\sin(x+180)\)

    • one year ago
  14. mathslover
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    oh k , got it!

    • one year ago
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