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abbyl94

  • one year ago

cos theta = 4/5, 0˚< theta < 90˚ use the information given to find sin2theta, cos2theta, and tan 2theta

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  1. satellite73
    • one year ago
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    you need \(\sin(\theta)\) so compute these do you know how to find it?

  2. abbyl94
    • one year ago
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    the identities?

  3. satellite73
    • one year ago
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    |dw:1358823887705:dw|

  4. alanli123
    • one year ago
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    sin 2 theta = 2 sin theta cos theta cos 2 theta = 2 cos ^2 theta - 1 tan 2 theta = sin 2 theta / cos 2 theta

  5. abbyl94
    • one year ago
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    do i plug in 4/5 where theta is?

  6. Azteck
    • one year ago
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    If costheta=4/5 then sintheta= 3/5 \[\sin2\theta=2\sin\theta \cos\theta\]

  7. satellite73
    • one year ago
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    there is a picture of an angle whose cosine is \(\frac{4}{5}\) you find the third side by pythagoras, or recalling the 3 - 4 - 5 right triangle this tells you \(\sin(\theta)=\frac{3}{5}\)

  8. abbyl94
    • one year ago
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    oh okay

  9. abbyl94
    • one year ago
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    so 2 sin theta = 2 sin 3/5 cos 4/5

  10. satellite73
    • one year ago
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    no do not make that mistake, it is a common one do not use \(\theta=\frac{4}{5}\) use \(\cos(\theta)=\frac{4}{5}\) so \[\sin(2\theta)=2\times \frac{4}{5}\times \frac{3}{5}\]

  11. satellite73
    • one year ago
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    no not the cosine and sine of those numbers, those numbers ARE the cosine and sine

  12. satellite73
    • one year ago
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    use the numbers themselves, they are your sines and cosines

  13. abbyl94
    • one year ago
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    okay thank you!

  14. satellite73
    • one year ago
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    your good now right?

  15. abbyl94
    • one year ago
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    im still confused a little ..

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