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## anonymous 3 years ago Folks, I'm trying to evaluate (1/2)sin(2arcsec(-8)) where arcsec is the inverse secant. The answer is supposed to be 3sqrt(7)/128. I'll post a sketch of what I've done so far.

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1. anonymous

|dw:1343155955658:dw|. I'm not sure how deal with the 2arcsec(-8)

2. anonymous

$arcsec(-8) = \frac{\pi}{2}+\arcsin(1/8)$ If that sounds weird, draw a sketch and you might notice why.

3. anonymous

It might be an equivalence, but how does that become 3sqrt(7)/128?

4. anonymous

Is there an identity I'm missing?

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