Posted by **Stacey grahaM** on Monday, May 3, 2010 at 11:50pm.

Tan theta 12/5 ,pi <theta<3pi/2

Find sin 2theta

- Trig -
**drwls**, Tuesday, May 4, 2010 at 2:07am
Think of a 5,12,13 right triangle. The principle angle (to the -y axis) is arcsin 12/13

Theta is in the third quadrant, and therefore

theta = pi + arcsin 12/13

sin 2theta = 2 sin theta cos theta

= 2*(-12/13)(-5/13) = 120/169 = 0.71006

Check: theta = 4.31760 radians

2 theta = 8.6352 radians

sin (2 theta) = 0.71006

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