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Pre Cal

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cos 75 deg

  • Pre Cal - ,

    cos(75) = cos(90-15) = sin(15)

    sin(15) = √((1-cos(30))/2)
    = √((1-√3/2)/2)
    = 1/2 √(2-√3)

    or

    sin(15) = sin(45-30)
    = sin45cos30 - cos45sin30
    = 1/√2(√3/2 - 1/2)
    = (√3-1)/(2√2)

    I'll leave it to you to demonstrate that the two values are equal . . .

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