被积函数 (2-x)[√(2x-x^2) - x] = (2-x)√(2x-x^2) - (2-x)x= (2-x)√[1-(1-x)^2] - (2-x)x= (1+1-x)√[1-(1-x)^2] - (2-x)x= (1-x)√[1-(1-x)^2] + √[1-(1-x)^2] - (2-x)x代入即得
