2m/5n²p-3n/4mp²=(8m²p-15n³)/20mn²p²3y/2x+2y+2xy/x²+xy=3y/2(x+y)+2xy/x(x+y)=3y/2(x+y)+2y/(x+y)=(3y+4y)/2(x+y)=7y/(2x+2y) 2x/x²-64y²-1/x-8y=2x/(x-8y)(x+8y)-1...3y/2x+2y+2xy/x²+xy这题我有不明白的，=3y/2(x+y)+2y/(x+y)=(3y+4y)/2(x+y)为什么3y加4y不是加2y的么3y/2x+2y+2xy/x²+xy=3y/2(x+y)+2xy/x(x+y)=3y/2(x+y)+2y/(x+y)=3y/2(x+y)+4y/2(x+y)=(3y+4y)/2(x+y)=7y/(2x+2y)还有一个疑问2x/x²-64y²-1/x-8y： =2x/(x-8y)(x+8y)-1/(x-8y) =(2x-x-8y)/(x-8y)(x+8y)不是（2x-1）的么为什么是（2x-x-8y）别怪我差，我实在是乱。呵呵，用点心读书。 2x/x²-64y²-1/x-8y=2x/(x-8y)(x+8y)-1/(x-8y)=2x/(x-8y)(x+8y)-(x+8y)/(x-8y)(x+8y)=(2x-x-8y)/(x-8y)(x+8y)=(x-8y)/(x-8y)(x+8y)=1/(x+8y)最后一个问题欧，就是=(2x-x-8y)/(x-8y)(x+8y)=(x-8y)/(x-8y)(x+8y)2x怎消去的=2x-x-8y=x-8y