sinα+cosα=三分之根号三(sinα+cosα)²=1/3sin²α+2sinαcosα+cos²α=1/31+2sinαcosα=1/32sinαcosα=1/3-1=-2/3sin2α=-2/3sin²2α=4/9cos²2α=1-sin²2α=1-4/9=5/9cos2α=-√5...