分式加减的几道题目求速度1 .(x+y)²/（x-z)(y-z) - (y+z)²/（x-z)(y-z) = 2.2x+3y/x-y+2y/y-x-3y/x-y=

1)=(x+z+2y)/(y-z)
2)=(2x^2-2xy-2y)/(x-y)

1,={(x+y)^2-(y+z)^}/(x-z)(y-z)=(x^2+2xy-z^2-2yz)/(x-z)(y-z)={((x-z)(x+z)+2y(x-z)}/(x-z)(y-z)=(x+z+2y)/(y-z)
2,=2x+(3y-2y-3y)/(x-y)=2x-2y/(x-y)=(2x^2-2xy-2y)/(x-y)