七年级数学上册第三章用字母表示数3-5去括号去括号时符号变化有何规律？素材（新版）苏科
难易度：★★★★★
关键词：去括号、符号变化、规律
答案：
如果括号外的因数是正数，去括号后原括号內各项的符号与原来的符号相同；如果括号外的因数是负数，去括号后原括号內各项的符号与原来的符号相反。
【举一反三】
典例：下面各题去括号错误的是（ ）
Ａ．－（6－）=－6＋![](https://wkrtcs.bdimg.com/rtcs/image?w=13&md5sum=5b30b9f89b2ac770910c59ac3feaedc1&sign=6dc01b340f&rtcs_flag=1&rtcs_ver=3&l=webapp&bucketNum=130&ipr={"t":"img","w":"13","h":"15","dataType":"png","c":"word/media/image1.png","imgOriW":13,"imgOriH":15})
Ｂ．2＋（－＋－）=2－＋－![](https://wkrtcs.bdimg.com/rtcs/image?w=17&md5sum=5b30b9f89b2ac770910c59ac3feaedc1&sign=6dc01b340f&rtcs_flag=1&rtcs_ver=3&l=webapp&bucketNum=130&ipr={"t":"img","w":"17","h":"15","dataType":"png","c":"word/media/image4.png","imgOriW":17,"imgOriH":15})
Ｃ．－（4－6＋3）=－2＋3＋3![](https://wkrtcs.bdimg.com/rtcs/image?w=16&md5sum=5b30b9f89b2ac770910c59ac3feaedc1&sign=6dc01b340f&rtcs_flag=1&rtcs_ver=3&l=webapp&bucketNum=130&ipr={"t":"img","w":"16","h":"41","dataType":"png","c":"word/media/image3.png","imgOriW":16,"imgOriH":41})
Ｄ．（＋）－（－＋）=＋＋－![](https://wkrtcs.bdimg.com/rtcs/image?w=13&md5sum=5b30b9f89b2ac770910c59ac3feaedc1&sign=6dc01b340f&rtcs_flag=1&rtcs_ver=3&l=webapp&bucketNum=130&ipr={"t":"img","w":"13","h":"15","dataType":"png","c":"word/media/image7.png","imgOriW":13,"imgOriH":15})
思路导引：按去括号的符号变化规律去分析判断。
标准答案：选C
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