Question 329736: How do I use reference angles to find the exact value of sin 240 DEG? I need to know the steps and the answers. I can't find it in my reading or my notes.
Answer by texttutoring(324)   (Show Source):
You can put this solution on YOUR website! 240 is 60 degrees more than 180 degrees.
On the grid with a unit circle, this would put it in the lower left quadrant.
The reference angle would be 60 degrees. You always start at 0 degrees and move around in a counter-clockwise direction.
Knowing that the reference angle is 60 degrees, you can then draw a triangle, which will be a special triangle of 30-60-90, which you should know the ratios for.
The sin of 60 is sqrt(3)/2, so the sine of 240 will be -sqrt(3)/2.
Recall the principle of CAST (which specifies which quadrants have positive trig values).
Hope this makes some sense. It would be easier if I could draw a picture. If you need some clarifications, just let me know.
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