TransendentialPI Group Title 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. one year ago one year ago

1. TransendentialPI Group Title

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

2. Uniquebum Group Title

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

3. TransendentialPI Group Title

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

4. TransendentialPI Group Title

Is there an identity I'm missing?