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#1

$Old$ November 9th, 2009, 03:04 AM

karldiesen $karldiesen is offline$

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$Default$ Trig question

If $cos(x)=(-3/4)$ and ∏<x<(3∏/2) find the exact value of $sin(x/2)$

How do I get to the answer without using a calculator?

The answer should be: sin(x)=√(7)/(2√2)

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#2

$Old$ November 9th, 2009, 03:34 AM

Gusbob $Gusbob is offline$

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$\cos(x) = 1 - 2\sin^2(\frac{x}{2})$

Now equate this to -3/4 and solve for sin(x/2). I'm sure it's a typo but it's $\sin\left(\frac{x}{2}\right) = \frac{\sqrt7}{2\sqrt2}$ , not sin(x)

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