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Math Help - Acute angle

  1. #1
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    Acute angle

    If [theta] is an acute angle with sin[theta]=3/5, find the exact value of cos2[theta].

    This is the last one I am stumped on.
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  2. #2
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by gretchen View Post
    If [theta] is an acute angle with sin[theta]=3/5, find the exact value of cos2[theta].

    This is the last one I am stumped on.
    Call theta = t for simplicity.

    cos^2(t) = 1 - 2*sin^2(t) = 1 - 2*(3/5)^2 = 1 - 2*9/25

    = 1 - 18/25 = 7/25

    -Dan
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  3. #3
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    some additional helps for you

    You may use the formula to solve the questions related to this as

    cos 2(theta)=cos^2 (theta) - sin^2 (theta)
    = 1- 2*sin^2 (theta)
    = 2*cos^2 (theta) - 1

    These are the formulas to solve the problem
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