届中考数学总复习专题教案5_中考数学总复习5

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课时．分式【课前热身】

x1x2x．当时，分式有意义；当时，分式的值

x1x为．．填写出未知的分子或分母：3x()y11222xyxyy2y1()xyxyyxxx1b1，，2，中，分式的个数是x133xy．计算：．代数式．．．．(ab)2计算2的结果为ab．b．a．1．【知识整理】

A的形式，如果除式中含BAA有，那么称为分式．若，则有意义；若

BBAA，则无意义；若，则BB1b分式：整式除以整式，可以表示成．分式的基本性质：分式的分子与分母都乘以或除以同一个不等于零的整式，分式的．用式子表示为约分：把一个分式的分子和分母的约去，这种变形称为分式的约分．

．通分：根据分式的基本性质，把异分母的分式化为的分式，这一过程称为分式的通分．分式的运算：用字母表示⑴加减法法则：①同分母的分式相加减：②异分母的分式相加减：⑵乘法法则：乘方法则：⑶除法法则：．易错知识辨析：在讨论分式问题，使分式有意义是前提，忽视这个前提，就容易出现各种各样的错误特别是求使得分式值为零的问题，最容易忽视分母不为零这个前提【例题讲解】例当时，分式式3无意义；1x3有意义；当时，分1x2x当时，分式9的值为零x3例（）已知x3，则x21x1x2112x14xy2y已知3，则代数式的值为xyx2xyy若，则11的值为a1b1m26m93m5例化简：m2m32m4m2例先化简，再求值：

112，其中222x2xx4x4x2xxx11，其中x3122x1x1x2x1【中考演练】5abx24x4．化简分式：，20a2bx2．3a()a21≠，25xy10axya4()x11x22x．计算：．分式

111，的最简公分母是．

2x3x2y24xy3．把分式x≠，≠中的分子、分母的x、y同时扩大倍，xy那么分式的值扩大倍缩小缩小不变．把分式xy≠，≠中的分子、分母的x、y同时扩大倍，xy1214那么分式的值扩大倍缩小缩小不变．如果，则xy4xyx．．．．

3yy

1214下列各式，正确的是yy2xyxy11020xyxyxxxyxy下列名式中，最简分式是34(xy)y2x2x2y2x2y222285(xy)xyxyxy(xy)

下列式

baab|ba|xy11；；；22caacabxyxyxyxy中正确的有xyxy个个个个已知两个分式：三个结论：①；②、互为倒数；③、互为相反数．请问哪个正确为什么x22x111先化简2，再取一个你认为合理的x值，代入求x1xx1411，，其中≠±．下面有2x22xx4原式的值已知，，，且，求acb1bcabac11的值abc