Calculus/Trig

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Expert: - 11/16/2009


Question
Suppose that cos θ = 3/5 and that θ is a Quadrant IV angle.  Find the exact value of sin θ.  Show some work/explanation.

Please help me!

Answer
Hi Cindy,
cos²θ + sin²θ = 1
sin²θ = 1 - cos²θ
sinθ = √(1 - cos²θ)
But,
cosθ = 3/5
So,
sinθ = √[1 - (3/5)²]
    = √[1 - (9/25)]
    = √(16/25)
    = ± 4/5
But in quadrant IV, sine is negative and so
sinθ = -4/5

Regards  

Calculus

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