作业帮先化简,再求值;[(2a-b/a b)-(b/a-b)]÷{(a-2b/a b) [ab/(a-b)2]},其中b/a=-1/2七下数学同步练浙教版期末综合性测试25题
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![先化简,再求值;[(2a-b/a b)-(b/a-b)]÷{(a-2b/a b) [ab/(a-b)2]},其中b/a=-1/2七下数学同步练浙教版期末综合性测试25题](/uploads/image/z/1811921-41-1.jpg?t=%E5%85%88%E5%8C%96%E7%AE%80%2C%E5%86%8D%E6%B1%82%E5%80%BC%3B%5B%282a-b%2Fa+b%29-%28b%2Fa-b%29%5D%C3%B7%7B%28a-2b%2Fa+b%29+%5Bab%2F%28a-b%292%5D%7D%2C%E5%85%B6%E4%B8%ADb%2Fa%3D-1%2F2%E4%B8%83%E4%B8%8B%E6%95%B0%E5%AD%A6%E5%90%8C%E6%AD%A5%E7%BB%83%E6%B5%99%E6%95%99%E7%89%88%E6%9C%9F%E6%9C%AB%E7%BB%BC%E5%90%88%E6%80%A7%E6%B5%8B%E8%AF%9525%E9%A2%98)
先化简,再求值;[(2a-b/a b)-(b/a-b)]÷{(a-2b/a b) [ab/(a-b)2]},其中b/a=-1/2七下数学同步练浙教版期末综合性测试25题
先化简,再求值;[(2a-b/a b)-(b/a-b)]÷{(a-2b/a b) [ab/(a-b)2]},其中b/a=-1/2
七下数学同步练浙教版期末综合性测试25题
先化简,再求值;[(2a-b/a b)-(b/a-b)]÷{(a-2b/a b) [ab/(a-b)2]},其中b/a=-1/2七下数学同步练浙教版期末综合性测试25题
先化简,再求值;［(2a-b/a+b）-（b/a-b)］÷{（a-2b/a+b）+［ab/(a-b)²］},其中b/a=-1/2
解,得：
［(2a-b)(a-b)-b(a+b)]/[(a+b)(a-b)］÷[(a-2b)(a-b)^2+ab(a+b)]/[(a+b)(a-b)^2]
==[(2a-b)(a-b)-b(a+b)]/[(a+b)(a-b)］* [(a+b)(a-b)^2]/[(a-2b)(a-b)^2+ab(a+b)]
==[(2a-b)(a-b)-b(a+b)](a-b)/ [(a-2b)(a-b)^2+ab(a+b)]
==2(a^3-3a^2b+2ab^2)/(a^3-3a^2b+7ab^2-2b^3)
因为b/a==-1/2
b==-a/2
把b带入2(a^3-3a^2b+2ab^2)/(a^3-3a^2b+7ab^2-2b^3),得
(2a^3+3a^3+a^3)/[(4a^3+6a^3+7a^3+a^3)/4]
==6a^3/([18a^3)/4]
==6a^3*(4/18a^3)
==4/3
答：
[(2a-b)/(a+b)-b/(a-b)]÷{ (a-2b)/(a+b)*[ab/(a-b)^2]
=[(2a-b)(a-b)/(a^2-b^2)-b(a+b)/(a^2-b^2)] ×{(a+b)*(a-b)^2 /[(a-2b)ab] }
=[(2a^2-3ab+b^2-ab-b^2)/(a^2-b^2)] ×(a+b)×(a-b)^2 /[(a-2b)ab]<...
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答：
[(2a-b)/(a+b)-b/(a-b)]÷{ (a-2b)/(a+b)*[ab/(a-b)^2]
=[(2a-b)(a-b)/(a^2-b^2)-b(a+b)/(a^2-b^2)] ×{(a+b)*(a-b)^2 /[(a-2b)ab] }
=[(2a^2-3ab+b^2-ab-b^2)/(a^2-b^2)] ×(a+b)×(a-b)^2 /[(a-2b)ab]
=(2a^2-4ab)×(a-b) /[(a-2b)ab]
=2a(a-2b)×(a-b)/[(a-2b)ab]
=2(a-b)/b
=2a/b-2
=2*1/(-1/2)-2
=-4-2
=-6
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