SOLUTION: If A is an obtuse angle in a triangle and sinA= 5/13, calculate the exact value of sin2A

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Question 938546: If A is an obtuse angle in a triangle and sinA= 5/13, calculate the exact value of sin2A
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
If A is an obtuse angle in a triangle and sinA= 5/13,
calculate the exact value of sin2A
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sin(2A) = 2*sin(A)*cos(A)
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If sin(A) = 5/13 in QII, cos(A) = -sqrt[13^2-5^2]]/13 = -12/13
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Ans: sin(2A) = 2(5/13)(-12/13) = -120/169 = -0.7100
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Cheers,
Stan H.
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