Isaac C. answered • 04/30/15
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You know the sin for special angles. The trick is to find 255 as the sum of two angles you know. When the angle ends in 255, then you know that one of the angles must be based on 45 degrees. So find the odd multiple of 45 closest to 255. In this case that is 225 (which is five times 45).
sin 255 = sin (225 + 30) = sin(225)cos(30) + sin(30)cos(225).
Using your knowledge of sin values for unit circle and rules about whether sin or cos is positive in a given quadrant ought to get you through the rest of this. If you don't know that part, you are going to have to study the unit circle again.
If instead, the number ends in 0, then try even or odd multiples of 30 degrees.
