SOLUTION: Please help me answer this and give some explanations for easy understanding.. Given: sin= -4/5 pi<theita<3pi/2 Find sin2theita and sin theita/2 Pls. reply as soon as possib

Question 782127: Please help me answer this and give some explanations for easy understanding..
Given:
sin= -4/5 pi Find sin2theita and sin theita/2
Pls. reply as soon as possible >_<
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Given:
sin= -4/5 pi Find sin2theita and sin theita/2
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Assuming you mean sin(x) = -4/5 in QIII
you would get cos(x) = -3/5
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Then sin(2x) = 2*sin(x)cos(x) = 2(-4/5)(-3/5) = 24/25
And sin(x/2) = sqrt[(1-(cos(x))/2]
= sqrt[(1+(3/5))/2] = sqrt[4/5] = (2/5)sqrt(5)
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Cheers,
Stan H.
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