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March 28, 2017

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cos(-11pi/12)

  • Trig - ,

    sometimes I find it easier to visualize these kind of angles in degrees
    π/12 radians = 15°,
    so -11π/12 = -165°
    and 165 = 120+45

    cos(-11π/12) = cos(-165° = cos(165°)
    = cos(120 + 45)
    = cos120cos45 - sin120sin45
    = (-1/2)(1/√2) - (√3/2)(1/√2)
    = (-1 - √3)/(2√2)
    or
    = (-√2 - √6)/4

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