Using the addition or subtraction formulas for sine: addition formula sin(s + t) = sin s cos t + cos s sin t or the subtraction formula: sin(s + t) =...

Using the addition or subtraction formulas for sine: addition formula sin(s + t) = sin s cos t + cos s sin t or the subtraction formula: sin(s + t) = sin s cos t - cos s sin t. What is the exact value of the expression cos(285 degrees)?Please show steps and give explanation so I can know how to do the other problems. I am mostly confused how to split up the number into manageable numbers that I know the specific value for. Like 30 degrees or 40 degrees.