有一列按规律排列的代数式：b，2b-a，3b-2a，4b-3a，5b-4a …，相邻两个代数式的差都是同一个整式．（1）按这个规律得到的第7个代数式是______．（2）若第4个代数式的值为8，则前7个代数式的和的值为______．
（1）根据题意得：第7个代数式是7b-6a；（2）∵4b-3a=8，∴b+（2b-a）+（3b-2a）+（4b-3a）+（5b-4a）+（6b-5a）+（7b-6a）=28b-21a=7（4b-3a）=56．故答案为：（1）7b-6a；（2）56
试题“有一列按规律排列的代数式：b，2b-a，3b-2...”；主要考察你对
等知识点的理解。
将四个数a、b、c、d排列成二行二列，两边各加一条竖直线，记成
=ab-cd，若
=6，则x=______．
对于任意不相等的两个实数a、b，定义运算※如下：a※b=
，那么8※12=______．
定义：如果一元二次方程ax2+bx+c=0（a≠0）满足a-b+c=0，那么我们称这个方程为“凤凰方程”．已知2x2-mx-n=0是关于x的凤凰方程，m是方程的一个根，则m的值为______．
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1.75亿学生的选择
(2a+b)(2a-b)+3(2a-b)的平方+3a(4a-3b)
寂寞绑票769
(2a+b)(2a-b)+3(2a-b)的平方+3a(4a-3b)=4a²-b²+3(4a²-4ab+b²)+12a²-9ab=4a²-b²+12a²-12ab+3b²+12a²-9ab=28a²-21ab+15b²
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其他类似问题
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＞＞＞先化简，再求值：（2a+b）（2a-b）+3（2a-b）2+3a（4a-3b），其中a=-1，b=..
先化简，再求值：（2a+b）（2a-b）+3（2a-b）2+3a（4a-3b），其中a=-1，b=2．
题型：解答题难度：中档来源：不详
原式=4a2-b2+3（4a2-4ab+b2）+12a2-9ab=4a2-b2+12a2-12ab+3b2+12a2-9ab=28a2-21ab+2b2，当a=-1，b=2时，原式=28-21×（-1）×2+2×4=28+42+8=78．
马上分享给同学
据魔方格专家权威分析，试题“先化简，再求值：（2a+b）（2a-b）+3（2a-b）2+3a（4a-3b），其中a=-1，b=..”主要考查你对&&整式的加减乘除混合运算&&等考点的理解。关于这些考点的“档案”如下：
现在没空？点击收藏，以后再看。
因为篇幅有限，只列出部分考点，详细请访问。
整式的加减乘除混合运算
加法、减法、乘法和除法，统称为四则运算。其中，加法和减法叫做第一级运算；乘法和除法叫做第二级运算。注意运算顺序，先做乘方，再做乘除，最做加减运算，如果有同类项，就合并同类项，要求结果必须是最简形式。 基本运算顺序：只有一级运算时，从左到右计算；有两级运算时，先乘除,后加减。有括号时，先算括号里的；有多层括号时，先算小括号里的。要是有平方，先算平方。在混合运算中，先算括号内的数，括号从小到大，然后从高级到低级。
发现相似题
与“先化简，再求值：（2a+b）（2a-b）+3（2a-b）2+3a（4a-3b），其中a=-1，b=..”考查相似的试题有：
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1.75亿学生的选择
有一列按规律排列的代数式b,2b-a,3b-2a,4b-3a,5b-4a.(1)用文字表述其中的规律是（2）若第四个代数式的值为8,则前七个代数式的和的值为
第n项等于n乘以b减去n减一与a 的积前七个代数式的和b+2b-a+3b-2a+4b-3a+5b-4a+6b-5a+7b-6a=(1+2+……+7)b-(1+2+……+6)a=28b-21a=7*(4b-3a)=7*8=56
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其他类似问题
这是一个首项是b,公差为b-a的等差数列2
因为这是一个等差数列，前2n-1项的和是第n项的2n-1倍
则前七项的和为第四项的七倍，即7*8=56
（1）后一项和前一项差为b-a（2）4b-3a=8
前7个代数式的和（b+7b-6a）x7/2=56
(1)后一项比前一项多d-a;(2)8*7=56(第三个+第五个=2倍第四个……)
（1）代数式=nb-（n-1)a
(2)b+2b-a+3b-2a+4b-3a+5b-4a+6b-5a+7b-6a
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