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教育头条 > 初中数学 > 初一数学计算中的8个易错点,导致低分的“罪魁祸首”!

初一数学计算中的8个易错点,导致低分的“罪魁祸首”!

初中数学 08-20 浏览量: 分享:
计算是数学中的硬功夫,计算能力不好,就算再会解题,也拿不到高分,毕竟数学考试看的是最后的答案,就算解题过程对了,答案错了也只能得步骤分!下面三好网小编整理了初一数学中常见的易错点,同学们一定要把握好,可以白捡20分!


易错点一:书写不规范,抄写错误

刚开始接触有理数计算,有的同学往往将-1+(-2)写成-1+-2,-x写成-1x,这些基本的书写规范要注意。甚至有同学常犯“抄错”的毛病,上行到下行、卷子到答题卡抄错,这些都属于我们熟悉的“低级错误”。

例如,这是某同学答题过程,你们有没有中枪呢?


针对这种情况,三好网小编建议:做题时,要细心;眼盯住,手别慌。(一定要认真)


易错点二:跳步,不愿意多写步骤

有些同学计算时,喜欢跳跃思维,不按“套路”解题,往往导致结果错误。做题时,一定要按步骤去计算,不能急于求成,要循序渐进,在保证正确率的前提下、熟练之后,才可以省略一些非关键的步骤。


针对这种情况,三好网小编建议:做题时,按步骤,不着急,不跳步!


易错点三:运算顺序出错,法则不熟悉

下面这位同学,没有按照运算法则的顺序进行计算,导致了失分。 
 
正确运算顺序:括号优先,先乘方,再乘除,最后加减。加减法为一级运算,乘除为二级运算,乘方、开方(以后会学到)为三级运算;同级运算从左到右,不同级运算,应该先三级运算,然后二级运算,最后一级运算;如果有括号,先算括号里的,先算小括号,再算中括号,最后大括号。

以上运算顺序可以简记为:“从小(括号)到大(括号),从高(级)到低(级),(同级)从左到右”。



针对这种情况,三好网小编建议:牢记口诀多练习,认真计算没问题!


易错点四:去括号,注意系数及符号变化

对于计算题,老师发现同学们去括号时,最容易犯错!同学们去括号时,一定要注意括号前面的系数和符号。去括号时,当括号前面有“-”,括号内的符号要发生改变;当括号前面有系数时,括号内的每一项都要与其相乘。  

例如,同学们在去括号时,经常会出现将5-(4-3)去括号变成5-4-3(应是5-4+3),将5(x+6)去括号变成5x+6(少乘一项)。这类问题很常见,不知道你是否中招了呢?



针对这种情况,三好网小编建议:牢记口诀多练习,认真计算没问题!


易错点四:去括号,注意系数及符号变化

对于计算题,老师发现同学们去括号时,最容易犯错!同学们去括号时,一定要注意括号前面的系数和符号。去括号时,当括号前面有“-”,括号内的符号要发生改变;当括号前面有系数时,括号内的每一项都要与其相乘。  

例如,同学们在去括号时,经常会出现将5-(4-3)去括号变成5-4-3(应是5-4+3),将5(x+6)去括号变成5x+6(少乘一项)。这类问题很常见,不知道你是否中招了呢?


针对这种情况,三好网小编建议:去分母,要遍乘,常数项,不遗漏!


易错点六:去分母时,要注意分子中隐藏的括号

解方程去分母时,一定要注意,当分子有几项相加(减)时,去掉分母后,分子是一个整体,记得这个整体有一个“隐形”的括号呦!  

下面这位同学,去分母时没有注意隐藏的括号,导致了最终结果的错误。


针对这种情况,三好网小编建议:去分母,先找最小公倍数,再添隐形的括号!


易错点七:移项时注意符号变化

一元一次方程解题时,除了去分母常见错误以外,移项时符号的改变也是同学们经常出现错误的地方!同学们一定要弄清楚,将一项移到等号另一边时(利用的是等式性质,相当于等式两边同加或者同减),符号要发生改变。一定要注意呦!  

例如, 3x-1=x-4移项整理3x-x=-4+1;下面这位同学,移项时就忘记了变号,同学们做题时要认真哦!



对这种情况,三好网小编建议:移项有学问,符号要改变!


易错点八:符号判断中“奇负偶正”问题

计算时,我们要先定符号,再定(绝对)值。符号的判断我们要借助“奇负偶正”法则进行判定。下面我们来总结下学过的“奇负偶正”:

(1)去符号问题。例如-(-2)=2;-[-(-2)]=-2。当"-"的个数为奇数时,最终结果只保留一个"-";当"-"的个数为偶数时,最终结果只保留一个"+"(正号可以省略)。
(2)有理数乘(除)法运算时符号判断。例如(-2)×(-3)=6;(-2)×(-3)×(-4)=-24.当负因数的个数为奇数时,结果为负;当负因数的个数为偶数时,结果为正。  
(3)乘方运算时,符号的判定。例如(-2)2=4;(-2)3=-8;(-2)n,当n为偶数时,(-2)n =2n;当n为奇数时,(-2)n=-2n  

掌握了“奇负偶正”的符号判断方法后,更关键的是要准确地找到底数。记住,当负数和分数做底数时,底数必须加括号。  

比如下面这位同学,将-42算成了16,他将底数看成了-4,而实际上的底数是4(如果底数是-4,那么写法应该是 (-4)2)。



针对这种情况,三好网小编建议:符号化简找底数,奇负偶正再跟上!


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