计算2m/5n²p-3n/4mp²

来源：学生作业帮编辑：作业帮分类：数学作业时间：2024/05/25 20:13:53

计算2m/5n²p-3n/4mp²
还有两题：3y/2x+2y+2xy/x²+xy
2x/x²-64y²-1/x-8y
就这三题，做起来有很多疑问。

2m/5n²p-3n/4mp²
=(8m²p-15n³)/20mn²p²
3y/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/(x-8y)
=(2x-x-8y)/(x-8y)(x+8y)
=(x-8y)/(x-8y)(x+8y)
=1/(x+8y)
再问： 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
再答： 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)
再问：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。
再答：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)
再问：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
再答： =2x-x-8y =x-8y

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