sinα的4次方+cosα的4次方=sinα的4次方+(1-sinα平方）^2=2sinα的4次方-2sinα平方+1 =1=>sin^2(α)[sin^2(α)-1]=0 =>sinαcosα=0(sinα+cosα)^2 = 1 +2sinαcosα= 1 => sinα+cosα = 1 或 -1...