2sinα-cosα=根号3sinαcosα = (2-根号3)sinα cos^2α=(2-根号3)^2 sin^2α=(7-4根号3) (1-cos^2α)(1+7-4根号3)cos^2α=7-4根号34(2-根号3)cos^2α=(2-根号3)^2cos^2α=1/2-根号3/4 = {(根号6-根号2)/4}^2cosα ...