Question 706988: If SinThetas = -4/5, and thetas terminates in QIII, find cosThetas. Found 2 solutions by stanbon, Alan3354:Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website! If SinThetas = -4/5, and thetas terminates in QIII, find cosThetas.
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sin(theta) = y/r = -4/5
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Since y = -4 and r = 5, solve for "x":
x^2 = r^2 - y^2
x = sqrt[5^2-4^2] = sqrt(9) = 3
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But x is negative in QIII, so x = -3
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Ans: cos(theta) = x/r = -3/5
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Cheers,
Stan H.
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