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Homework Help: Simplify trigno expression

  1. Apr 6, 2010 #1
    1. The problem statement, all variables and given/known data

    cos(2 * arcsin(2x))

    Use a triangle to simplify each expression. Where application, state the range of x's for which the simplification holds.

    2. Relevant equations

    cos(2t) = cos^2(t) - sin^2(t) = 1-2sin^2(t) = 2cos^2(t) - 1

    3. The attempt at a solution

    My attempt was the following


    let arcsin(2x) = delta (or t)
    so cos(2t) = double angle formula

    cos2(t) = 1-2sin^2(t)
    replace t, and by definition sin(arcsinx) = x
    so i think i got 1-2*(2x)^2 = 1-8x^2

    please verify for me

    thank you
  2. jcsd
  3. Apr 6, 2010 #2


    Staff: Mentor

    That's what I get.
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