八年级数学分式课件5.ppt.ppt

分式复习二分式的加减同分母相加异分母相加 A CBA CA B??? AD AC BD AD CA AD BD D CA B?????通分{ 1、通分: ?? 52 29 7 12 2342aab cab ·268 16 3 12 222 xxxx xxx ???????,,2、的最简公分母是 21 1322x xx???、3、的最简公分母是 aabb bbab cb 223242 ( )() ,( )()() ?????, 4、计算: x xx x?????1 121 1)2( aa 34)1(? 2 121 1)3(?????x xx x???????????????? 12 11221 21??????????xx xxxx xx???????? 12 1221 23 2 2??????????xx xxxx xx2 123 2 2?????xx xx 1 121 1)4( 2?????x xx x???????????? 11 11211 1?????????xx xxxx x???????? 11 1211 1 2?????????xx xxxx x???? 11 222 2??????xx xx1 222 2 2?????x xx 1 122)5(????x xx?? 1 122?????x xx???? 1 121 12???????x x x xx1 1 2????x xx (6)、计算: xy x yyx xx yx????? 2 2 )2(解: xy x yyx xx yx????? 2 2)()()( ) )(( 2 2yxx yyxx xyxx yxyx????????xy x yxyx????? 2 22220?(7)当 x = 200 时,求的值. xxx xx x13 63 2?????解: xxx xx x13 63 2?????)3( 3)3( 6)3( 2????????xx xxx xxx x)3( 9 2???xx x)3( )3 )(3(????xx xxx x3??当x = 200 时,原式= 200 3200 ?200 203 ? 10 3 1 10 3 2 10 3 1 2 2 2 ???????????xx xxx xxx x1 1 3 2????a a aa4练一练