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Math Help - Help on Trig Questions.

  1. #1
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    Help on Trig Questions.

    1. Use a Sum or difference identity to find the exact value of sin285degrees

    2. If tanX = -3/4 and 90<x<180, find cosX (the 90 and 180 are degrees)

    3. If (tanX)(cscX) = 3, find value of cosX

    4. If tanX= 3/4 and 180<X<270, find the exact value of sin2X

    5. Find the value of tan(A+b) if cosA = 13/5, tanB = 3/4, and 0<A<90
    Last edited by mr fantastic; December 17th 2010 at 02:17 AM. Reason: Title.
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  2. #2
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    Quote Originally Posted by Joker View Post
    [1. Use a Sum or difference identity to find the exact value of sin285degrees
    \sin\left(285^{\circ}\right) = \sin\left(180^{\circ}+105^{\circ}\right) = -\sin\left(105^{\circ}\right) = -\sin\left(60^{\circ}+45^{\circ}\right)

    Expand that using the 'sum or difference' formula for sine.

    2. If tanX = -3/4 and 90<x<180, find cosX (the 90 and 180 are degrees)
    Pythagoras' theorem: If \tan{x} = \frac{-3}{4}, then \cos{x} = \frac{4}{\sqrt{(-3)^2+(4)^2}} = ...

    3. If (tanX)(cscX) = 3, find value of cosX
    {\tan{x}}{\csc{x}} = \frac{\sin{x}}{\cos{x}\sin{x}} = \frac{1}{\cos{x}}, so \cos{x} = \cdots

    4. If tanX= 3/4 and 180<X<270, find the exact value of sin2X
    Write \tan{x} in terms of \cos{x} and \sin{x} and use the identity \sin{2x} = 2\sin{x}\cos{x}.

    5. Find the value of tan(A+b) if cosA = 13/5, tanB = 3/4, and 0<A<90
    Write \tan\left(a+b\right) = \frac{\sin\left(a+b\right)}{\cos\left(a+b\right)}, use the 'sum-difference' formulas on both the
    numerator and the denominator, and write \tan{b} in terms of sine and cosine.
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