cosx = -5/13 where pi/2 < x < pi find

a) sin2x

any idea how to do this?

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- Dec 10th 2008, 04:54 PMmike41cosx = -5/13 ... find sin2x
cosx = -5/13 where pi/2 < x < pi find

a) sin2x

any idea how to do this? - Dec 10th 2008, 05:06 PMskeeter
find the value of $\displaystyle \sin{x}$ using the value they gave you for $\displaystyle \cos{x}$ by sketching a reference triangle in quad II.

then use the double angle identity ...

$\displaystyle 2\sin{x} \cos{x} = \sin(2x)$ - Dec 10th 2008, 05:24 PMmike41
wow thank you skeet

thought there was another way to solve it