SOLUTION: If tanθ= 3/8, and θ in quadrant 111, find the exact value of cos2θ
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Question 834740: If tanθ= 3/8, and θ in quadrant 111, find the exact value of cos2θ
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
If tanθ= 3/8, and θ in quadrant 111, find the exact value of cos2θ
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QIII has x < 0 and y < 0
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Since tan = y/x, y = -3 and x = -8
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r = sqrt[3^2+8^2] = sqrt[9+64] = sqrt[73]
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Your Problem:
cos(2t) = 2sin^2(t)-1 = 2(y/r)^2-1 = 2(-3/sqrt(73)^2)-1
= 2(9/73) - 1 = (18/73)-1 = -0.7534
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Cheers,
Stan H.
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