急!一道超难数学题(初二下)已知(1/a)-(1/b)=3,求分式(2a+3ab-2b)/(a-ab-b)的值
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急!一道超难数学题(初二下)已知(1/a)-(1/b)=3,求分式(2a+3ab-2b)/(a-ab-b)的值
急!一道超难数学题(初二下)
已知(1/a)-(1/b)=3,求分式(2a+3ab-2b)/(a-ab-b)的值
急!一道超难数学题(初二下)已知(1/a)-(1/b)=3,求分式(2a+3ab-2b)/(a-ab-b)的值
1/a-1/b=2
(b-a)/ab=2
b-a=2ab
原式=[(2a-2b)-ab]/[(a-b)-3ab]
=[-2(b--a)-ab]/[-(b-a)-3ab]
=[-2*2ab-ab]/[-2ab-3ab]
=[-5ab]/[-5ab]
=1
祝你学习天天向上,加油!
分子分母同时除以ab可得
=[2(1/a-1/b)+3]/(1/a-1/b-1)
=9/2.
(2a+3ab-2b)/(a-ab-b)
=[(2a+3ab-2b)/(ab)]/[(a-ab-b)/(ab)]
=[(2/b+3-2/a)]/[(1/b-1-1/a)]
=[-2(1/a-1/b)+3)][-(1/a-1/b)-1]
=(-2*3+3)/(-3-1)
=3/4
∵ 1/a-1/b=3
∴ b-a=3ab
a-ab-b=a-b-ab
=-3ab-ab
=-4ab
2a+3ab-2b=2(a-b)+3ab
=2×(-3ab)+3ab
=-3ab
∴原式=-4ab/(-3ab)
= 4/3
分子分母同时除以ab。答案为 3/4。
(1/a)-(1/b)=3
(b-a)/ab=3
3ab=b-a
(2a+3ab-2b)/(a-ab-b)
=[-2(b-a)+3ab]/[-(b-a)-ab]
=(-2*3ab+3ab)/(-3ab-ab)
=-3ab/-4ab
=3/4