SOLUTION: what is cos alpha when sin is 4/5 and tan is less than zero

Question 717656: what is cos alpha when sin is 4/5 and tan is less than zero
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
what is cos alpha when sin is 4/5 and tan is less than zero
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If sin is 4/5 the angle is in QI or in QII
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If tan is less than zero, the angle must be in QII where x is neg and y is pos:
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If sin = y/r = 4/5, y = 4 and r = 5
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Then x = -sqrt(5^2-4^2) = -sqrt(9) = -3
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So:
r = 5
x = -3
y = 4
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Ans: cos(theta) = x/r = -3/5
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Cheers,
Stan H.
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