cos（π／6 －α）＝1／3cosπ/6cosα+sinπ/6sinα=1/3根号3/2cosα+1/2sinα=1/3两边平方得：3/4cos^2α+1/4sin^2α+根号3/2sinαcosα=1/91/4(cos^2α+1/4sin^2α) + 1/2cos^2α +根号3/4 sin2α = 1/91/4(cos^2...