we can not use calculators, and we needed to know these two formulas:
cos(alpha+-beta)=cos(alpha)cos(beta)-+sin(alpha)sin(beta)
sin(alpha+-beta)=sin(alpha)cos(beta)+-cos(alpha)sin(beta)
Ex. Find the exact value of sin 75.
sin(45+30)=sin45cos30+cos45sin30
squared root of 2 over 2 times one half plus squared root of 2 over 2 times squared root of 3 over 2=squared root of two plus six over four
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