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Homework Help: Trigonometric Identities

  1. Apr 26, 2016 #1
    1. The problem statement, all variables and given/known data

    2sin2θ - 1 = sin2θ - cos2θ
    2. Relevant equations

    3. The attempt at a solution
    I am unsure of how to prove these.

    So far all I have is

    Left side= 2sin2θ - 1

    And I know that right side is equal to 1.

    But otherwise not sure where to go from there.
  2. jcsd
  3. Apr 26, 2016 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    The right side is not 1.

    2x2 ≠ x2⋅x2 .

    So certainly, 2sin2θ ≠ sin2θ ⋅sin2θ
  4. Apr 26, 2016 #3
    I see where I went wrong now.
  5. Apr 26, 2016 #4
    Would I change right side to sin^2x - 1 - sin^2x?
  6. Apr 26, 2016 #5


    Staff: Mentor

    It's much simpler than this, and there is no need whatever for double-angle identies. What identities do you already know?
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