分式乘除的计算

题目

分式乘除的计算
1.(-n^2/2m)*(4m^2/5n^3)
2.(y/7x)/(-2/x)
3.-8xy/(2y/5x)
4.(a^2-4)/(a^2-2a+1)*(a^2-1)/(a^2-1/a^2+4a+4)
5.(5b^2/3ac)/(-10bc/21a)
6.(12xy/5a)/(-8x^2y)
7.(x^2-x/x-1)/(4-x)
*号为乘号

答案

1.(-n^2/2m)*(4m^2/5n^3)
=-4m^2n^2/(10mn^3)
=-2m/(5n)
2.(y/7x)/(-2/x)
=xy/(-14x)
=-y/14
3.-8xy/(2y/5x)
=-40x^2y/2y
=-20x^2
4.(a^2-4)/(a^2-2a+1)*(a^2-1)/(a^2-1/a^2+4a+4)
=(a+2)(a-2)(a+1)(a-1)/[(a-1)^2(a+2)^2]
=(a-2)(a+1)/(a-1)(a+2)
=(a^2-a-2)/(a^2+2a-2)
5.(5b^2/3ac)/(-10bc/21a)
=(105ab^2)/(-30abc^2)
=-7b/(2c^2)
6.(12xy/5a)/(-8x^2y)
=12xy/(-40ax^2y)
=-3/(10ax)
7.(x^2-x/x-1)/(4-x)
=x(x-1)/[(x-1)(4-x)
=x/(4-x)