化简 7.6a+6.8b-2.8a-6b 12a-4a+7b-b

(3a-6b)/(a+b) - (5a-6b)/(a-b) - (4a-5b)/(a+b) - (7a-8b)/(a-b (3a-6b/a+b）-(5a-6b/a-b)-(4a-5b/a+b)-(7a-8b/b-a) a+b>a-b, (a-b)(a b) a/b-b/a 3a/a-4b +a+b/4b-a -7b/a-4b (a-b)(-a-b)化简? a-b>a,a+b 化简：{[(2a-b)/(a+b)]-[b/(a-b)]}÷[(a-2b)/(a+b)] 化简(2a-b/a+b-b/a-b)除以a-2b/a +b 化简(2a-b/a+b-b/a-b)除以a-2b/a+b 计算：((a+b)(a-b)-(a-b)^2+2b(a-b))/4(a-b)