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Math Help - Help needed on trigonometric proofs

  1. #1
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    Help needed on trigonometric proofs

    i was wondering if ANYONE could help me with some proofs i missed a couple days of trig. and im totally lost so here they are

    1. 1-cos(2a)/sin(2a)=tana

    2. cos(2a)= 1-tan^2a/1+tan^2a

    3. tan(2a)= 2/cota-tana

    thanks in advance
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  2. #2
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    Quote Originally Posted by bkstudent14 View Post
    i was wondering if ANYONE could help me with some proofs i missed a couple days of trig. and im totally lost so here they are

    1. 1-cos(2a)/sin(2a)=tana
    Hi

    \frac{1-\cos(2a)}{\sin(2a)} = \frac{1-(1-2\sin^2a)}{2\sin a \cos a} = \frac{2\sin^2a}{2\sin a \cos a} = \tan a

    As usual my advice is
    1) learn ans know perfectly the trig identities
    2) practice a lot
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  3. #3
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    Quote Originally Posted by bkstudent14 View Post
    2. cos(2a)= 1-tan^2a/1+tan^2a
    \frac{1-\tan^2a}{1+\tan^2a} = \frac{1-\frac{\sin^2a}{\cos^2a}}{1+\frac{\sin^2a}{\cos^2a}  } = \frac{\cos^2a-\sin^2a}{\cos^2a+\sin^2a} = \cos^2a-\sin^2a = \cos(2a)
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