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Math Help - Differentiating with parametric equations

  1. #1
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    Differentiating with parametric equations

    For part of my parametric eqn i need to differentiate 3-2cos2 theta, when i do this i get 2-sin2 theta, but the answers says 4sin2 theta, what am i doing wrong
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  2. #2
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    Re: Differentiating with parametric equations

    Quote Originally Posted by johnreal View Post
    For part of my parametric eqn i need to differentiate 3-2cos2 theta, when i do this i get 2-sin2 theta, but the answers says 4sin2 theta, what am i doing wrong
    (3-2\cos \2\theta)'=3'-(2\cdot (\cos \2\theta)'+2' \cdot \cos \2 \theta)=

     = 0-(-4\cdot \sin \2 \theta +0)= 4 \cdot \sin 2 \theta
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  3. #3
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    Re: Differentiating with parametric equations

    Thanks alot this helped *slaps face* Product Rule, ive worked out most of it and ive reached sin2 theta/cos theta, i did that by having 4sin2 theta/4cos theta and cancelling the fours, im supposed to get 2 sin theta, did i do some thing wrong?
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  4. #4
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    Re: Differentiating with parametric equations

    Quote Originally Posted by johnreal View Post
    Thanks alot this helped *slaps face* Product Rule, ive worked out most of it and ive reached sin2 theta/cos theta, i did that by having 4sin2 theta/4cos theta and cancelling the fours, im supposed to get 2 sin theta, did i do some thing wrong?
    \sin 2\theta = 2 \sin \theta \cdot \cos \theta
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