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Trigonometric equation for stress

  1. Jun 24, 2016 #1
    1. The problem statement, all variables and given/known data
    is the circled part wrong ?
    0bDsABg.jpg
    2. Relevant equations


    3. The attempt at a solution
    how could 0.5 sin2theta = ( 1 + cos2theta ) / 2 ?
     
  2. jcsd
  3. Jun 24, 2016 #2

    SteamKing

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    It's a trig identity. Look up "Half-Angle" formulas:

    https://en.wikipedia.org/wiki/List_of_trigonometric_identities
     
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