88问答网
所有问题
1x2+2x3+3x4+...+ n的计算方法
如题所述
举报该问题
推荐答案 2024-01-04
求1x2+2x3+3x4+……+n(n+1)
注意到:
(n+1)^3-n^3=3n^2+3n+1
则可得:
n(n+1)=[(n+1)^3-n^3]/3-1/3
那么有:
1×2=(2^3-1^3)/3-1/3
2×3=(3^3-2^3)/3-1/3
……
累加可得:
所求算式
=[(n+1)^3-1^3]/3-n/3
=(n^3+3n^2+3n-n)/3
=n(n+1)(n+2)/3
温馨提示:答案为网友推荐,仅供参考
当前网址:
http://88.wendadaohang.com/zd/BSK1V11KtSBtMBBSBg.html
其他回答
第1个回答 2024-01-04
1x2+2x3+3x4+...+n(n+1)
=(1²+1)+(2²+2)+(3²+3)+...+(n²+n)
=(1²+2²+....n²)+(1+2+...+n)
自然数列和自然数平方数列的求和公式知道吧
自然数平方数列求和公式Sn=n(n+1)(2n+1)/6
自然数列求和公式Sn=n(n+1)/2
两个相加化简得和=n(n+1)(n+2)/3
相似回答
1x2+2x3+3x4
…+10x11 1x2x3+2x
3x4+
3x4x5+…7x8x9写
答:
1x2+2x3+3x4+…+n(n+1)=1x(1+1)+2x(2+1)+3x(3+1)+…n(n+1)
=(1^2+2^2+3^2+…+n^2)+(1+2+3+…+n)=n(n+1)
(2n+1)/6+n(n+1)/2 =n(n+1)[(2n+1)+3]/6 1x2+2x3+3x4+…+10x11 =10x(10+1)x[(10x2+1)+3]/6 =110x4 =440 ...
1x2
十
2x3
十
3x4
十…...十1o0x101
答:
应用公式 1+
2+3+.+n
=1/2*n(n+1)1^2+2^2+3^2+...+n^2=1/6n(n+1)(2n+1)
1x2
十
2x3
十
3x4
十…...十100x101 =1x(1+1)十2x(2+1)十3x(3+1)十…...十100x(100+1)=(1^2+2^2+3^
2+.+
100*2)+(1+2+3+...+100)=1/6*100*101*201+1/2*101*100 =1/6*10...
1x2+2x3+3x4+
4x5
+.+n
(n+1)等于多少?急救! 请写下过程,谢谢
答:
1x2+2x3+3x4+…+n(n+1) =1^2+1+2^2+2+3^2+3+…+n^2+n
=(1^2+2^2+3^2+…+n^2)+(1+2+3+…+n) =1/6*n(n+1)(2n+1)+1/2*n(n+1) =1/6*n(n+1)(2n+1+3)(提取公因式) =1/3*n(n+1)(n+2)
请问这道题怎么做?
答:
=(n(
n+
1)(n+2)-(n-1)n(n+1))/3 所以1×2+2×3+…+ n(n+1)=n(n+1)(n+2)/3 (3)1001×1002+1002×1003···+2013×2014 =
1x2+2x3+3x4+
...+2013x2014-(1x2+2x3+3x4+...+1000x1001)=2013x2014x2015/3-1000x1001x1002/3 =2723058910-334334000 =2388724910 ...
1x2+2x3+3x4+
4x5
+.+n
(n+1)等于多少?急救! 请写下过程,谢谢
答:
1x2+2x3+3x4+
…+n(
n+
1) =1^2+1+2^2+2+3^2+3+…
+n
^2+n =(1^2+2^2+3^2+…+n^2)+(1+2+3+…+n) =1/6*n(n+1)(2n+1)+1/2*n(n+1) =1/6*n(n+1)(2n+1+3)(提取公因式) =1/3*n(n+1)(n+2)
1x2+2x3+3x4+
4x5+……+10x11 我要过程!!!
答:
1x2+2x3+3x4+
4x5+……+n(
n+
1)=1²+2²+3²+...
+n
²+(1+2+3+...+n)=n(n+1)(2n+1)/6+n(n+1)/2 =n(n+1)(n+2)/3 1x2+2x3+3x4+4x5+……+10x11 =10×11×12/3 =440
1x2
2x3
3x4
...
n
(n 1)=?过程
答:
1x2+2x3+3x4+
...+n(n+1)=1^2+1+2^2+2+3^2+3+...+n^2+n =1+2+...
+n+
(1^2+2^2+...+n^2)=(1+n)n/2+n(n+1)(2n+1)/6 =n(n+1)/2*(1+(2n+1)/3)=n(n+1)(2n+5)/6
1x2+2x3+3x4+
4x5+...
+n
(
n+
1)=?(n为正整数)
答:
回答:解 n(
n+1
)=n²+n ∴原式 =
1+1
²+2+2²+3+3²+……
+n+n
² =(
1+2+3+
……+n)+(1²+2²+3²+……+n²) =(1+n)n÷
2+1
/6n(n+1)(2n+1) =n(n+1)[1/2+1/6(2n+1)] =n(n+1)(1/3n+2/3) =1/3n...
大家正在搜
1x2十2x3十3x4推算过程
1x2十2x3十3x4十公式
f(x+1)=x²-3x+2
2x+1-2=x+2怎么解
2x-3=x+3解方程
lim2x+3/2x+1
3x(x-1)=2-2x
x2-3x+1=0
2x-3=x+3