z/x=z/u u/x+z/v v/x=2ulnv ×1+u²/v × 2xy=2(x+y)ln(x²y)+2(x+y)²/xz/y=z/u u/y+z/v v/y=2ulnv ×1 +u²/v ×x²=2（x+y）ln(x²y)+(x+y)²/y
