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问题: [2(a+b)/3(a-b)]-[ab/(a+b)(a-b)]=?

解答:

[2(a+b)/3(a-b)]-[ab/(a+b)(a-b)]=?

[2(a+b)/3(a-b)]-[ab/(a+b)(a-b)]
=[2(a+b)*(a+b)/3(a+b)(a-b)]-[3ab/3(a+b)(a-b)]
=[2(a+b)^2-3ab]/[3(a+b)(a-b)]
=(2a^2+4ab+2b^2-3ab)/[3(a+b)(a-b)]
=(2a^2+ab+2b^2)/[3(a^2-b^2)]