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Math Help - trig

  1. #1
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    trig

    can someone help me here? i know these are simple but i can't get it. Find sin(x/2) when cos(x)=3/7. and find cos(x/2) when sin(x)=5/12
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by jarny View Post
    can someone help me here? i know these are simple but i can't get it. Find sin(x/2) when cos(x)=3/7. and find cos(x/2) when sin(x)=5/12
    use the half-angle formulas:

    \sin \frac x2 = \pm \sqrt{\frac {1 - \cos x}2}

    and

    \cos \frac x2 = \pm \sqrt{\frac {1 + \cos x}2}


    also, \sin^2 x + \cos^2 x = 1 will come in handy for the second one
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