(2/3a)-[2/(a+b)]{[(a+b)/3a]-a-b}÷[(a-b)/a]

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(2/3a)-[2/(a+b)]{[(a+b)/3a]-a-b}÷[(a-b)/a]

(2/3a)-[2/(a+b)]{[(a+b)/3a]-a-b}÷[(a-b)/a]
(2/3a)-[2/(a+b)]{[(a+b)/3a]-a-b}÷[(a-b)/a]

(2/3a)-[2/(a+b)]{[(a+b)/3a]-a-b}÷[(a-b)/a]
原式=2/3a-[2/(a+b)]{[(a+b)/3a]-(a+b)}÷[(a-b)/a]
乘进去
=2/3a-[2/3a-2]×[a/(a-b)]
=2/3a-(2-6a)/3a×[a/(a-b)]
=2/3a-(2a-6a^2)/3a(a-b)
=(2a-2b-2a+6a^2)/(3a^2-3ab)
=(-2b+6a^2)/(3a^2-3ab)