15.2.2分式的加减(二)复习回顾1、分式的加减:bcabcbabdbcadbdbcbdaddcba2、分式的乘除bdacdcbabcadcdbadcba口算aaa15123mm31xyayxayxxyxy(4)(2)(3)(1)0m4yxa21(1)异分母的分数如何加减?(2)你认为异分母分式的加减应该如何进行?比如:如何计算?aa413(通分,将异分母的分数化为同分母的分数)计算:abcabba43326522解:原式=cbaabcbaaccbabc2222221291281210cbaabacbc22129810先找出最简公分母,再正确通分,转化为同分母的分式相加减。•计算:4122bbababaxyyxxyyx22222.)2(mmmm34225211112xxxnmmnmnmm2121)3(试一试xxxxxxxx4)44122)(1(222111)12.(1)2(2xxxxxx24422222yxyxyxyxyx2,25.2yx先化简,再求值:,其中