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TransendentialPI
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.
|dw:1343155955658:dw|. I'm not sure how deal with the 2arcsec(-8)
\[arcsec(-8) = \frac{\pi}{2}+\arcsin(1/8)\] If that sounds weird, draw a sketch and you might notice why.
It might be an equivalence, but how does that become 3sqrt(7)/128?
Is there an identity I'm missing?