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Math Help - MY brain is killing me! Help guys! TRIG of Doom!

  1. #1
    Newbie
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    Talking MY brain is killing me! Help guys! TRIG of Doom!

    If sin x = 0.3 , cos a= 0.5 and tan b = 2.4 and x, a, b are in first quadrant find value of following:

    cos ( π - x)

    sin ( π - a)

    --------------------------------------

    If x = π / 12 , 3 sin 2x is equal to...

    ?

    ________________________________

    Help appreciated.
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  2. #2
    Newbie DavePercy's Avatar
    Joined
    Feb 2008
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    You can use the identity \sin^2 x + \cos^2 x = 1 to get \cos x = \pm \sqrt{1-.3^2} and \sin a = \pm \sqrt{1-.5^2}. (Use the positive root in this case since the angles are all in the first quadrant.) Once you have these you can use the properties cos(pi-x) = -cos x and sin(pi-x) = sin x.

    For the second problem just plug in the given x value and use special right triangles or special unit circle values to evaluate it. 3 sin (2pi/12) = 3 sin (pi/6) = 3 * 1/2
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