sin(45`+30`)=sin75`=根号2/2(1/2+根号3/2)
sin(74`)=sin(37`+37`)=2sin37`*cos37`=2*0.6*0.8=0.96
cos(45`+30`)=cos75`=根号2/2(根号3/2-1/2)
cos(74`)=1-2sin37`^2=1-0.72=0.28
sin(75`-74`)=sin1`=根号2/2(1/2+根号3/2)*0.28-根号2/2(根号3/2-1/2)*0.96
sin3`=4sin1`^2-3sin1`=4*[根号2/2(1/2+根号3/2)*0.28-根号2/2(根号3/2-1/2)*0.96]-3[根号2/2(1/2+根号3/2)*0.28-根号2/2(根号3/2-1/2)*0.96]
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