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,人教版 七年级,下,第,9,章 不等式,与不等式组,9.1.2,不等式的性质,C,C,1,2,3,4,5,A,D,6,7,8,D,答 案 呈 现,温馨,提示,:,点击,进入,讲评,习题链接,9,B,10,C,A,【,2020,杭州】,若,a,b,,则,(,),A,a,1,b,B,b,1,a,C,a,1,b,1,D,a,1,b,1,C,1,由,a,3,b,1,,可得结论,(,),A,a,b,B,a,3,b,3,C,a,1,b,3,D,a,1,3,y,,则下列不等式中一定成立的是,(,),A,x,y,0,B,x,y,0,C,x,y,0,D,x,y,0,若,m,n,,则下列不等式不一定成立的是,(,),A,m,2,n,2,B,2,m,2,n,D,4,【,点拨,】,A.,不等式的两边都加,2,,不等号的方向不变,故,A,正确;,B.,不等式的两边都乘,2,,不等号的方向不变,故,B,正确,;,C,.,不等式的两边都除以,2,,不等号的方向不变,故,C,正确,D,5,【教材,P,120,习题,T,4,变式】【,2021,河北】,已知,a,b,,则一定有,4,a,4,b,“ ”,中应填的符号是,(,),A,B,C,D,6,B,7,C,8,A,【,点拨,】,a,b,,,当,a,0,时,,a,2,ab,,,当,a,0,时,,a,2,ab,,故结论,错误;,a,b,,,当,|,a,|,|,b,|,时,,a,2,b,2,,,当,|,a,|,|,b,|,时,,a,2,b,2,,故,结论,错误;,a,b,,,b,0,,,a,b,2,b,,故结论,错误;,a,b,,,b,0. ,a,b,0,,,比较大小:,(1),如果,a,1,b,2,,那么,a,_,b,.,(2),试比较,2,a,与,3,a,的大小:,当,a,0,时,,2,a,_3,a,;,当,a,0,时,,2,a,_3,a,;,当,a,0,时,,2,a,_3,a,.,9,(3),试比较,a,b,与,a,的大小,解:,当,b,0,时,,a,b,a,;,当,b,0,时,,a,b,a,;,当,b,0,时,,a,b,a,.,(4),试判断,x,2,3,x,1,与,3,x,1,的大小,解,:,x,2,0,,,x,2,3,x,1,3,x,1.,10,解:由已知得,1,a,0,,即,a,1,.,则,|,a,1|,|,a,2|,a,1,a,2,2,a,1.,
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