tính : 1+1\2*(1+2)+1\3*(1+2+3)+...+1\20*(1+2+3+...+20)
K
Khách
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
Những câu hỏi liên quan
30 tháng 1
\(1+\dfrac{1}{2}\left(1+2\right)+\dfrac{1}{3}\left(1+2+3\right)+...+\dfrac{1}{20}\left(1+2+3+...+20\right)\)
\(=1+\dfrac{1}{2}\cdot\dfrac{2\cdot3}{2}+\dfrac{1}{3}\cdot\dfrac{3\cdot4}{2}+...+\dfrac{1}{20}\cdot\dfrac{20\cdot21}{2}\)
\(=1+\dfrac{3}{2}+\dfrac{4}{2}+...+\dfrac{21}{2}\)
\(=\dfrac{2+3+4+...+21}{2}=\dfrac{\left(21+2\right)+\left(3+20\right)+...+\left(10+13\right)+\left(11+12\right)}{2}\)
\(=\dfrac{23+23+...+23}{2}=\dfrac{23\cdot10}{2}=23\cdot5=115\)
PN
0
DT
0
IM
0
H
0
TQ
1
2 tháng 3 2017
\(B=1+\frac{1}{2}\left(1+2\right)+\frac{1}{3}\left(1+2+3\right)+...+\frac{1}{20}\left(1+2+3+...+20\right)\)
\(=1+\frac{1}{2}.\frac{2\left(2+1\right)}{2}+\frac{1}{3}.\frac{3\left(3+1\right)}{2}+...+\frac{1}{20}.\frac{20\left(20+1\right)}{2}\)
\(=\frac{2}{2}+\frac{2+1}{2}+\frac{3+1}{2}+...+\frac{20+1}{2}\)
\(=\frac{2}{2}+\frac{3}{2}+\frac{4}{2}+...+\frac{20}{2}\)
\(=\frac{2+3+4+...+20}{2}=\frac{\frac{20\left(20+1\right)}{2}-1}{2}=\frac{209}{2}\)
KT
0
A
1
29 tháng 4 2022
\(1+\dfrac{1}{2}\left(1+2\right)+\dfrac{1}{3}\left(1+2+3\right)+...+\dfrac{1}{20}\left(1+2+3+...+20\right)\)\(=1+\dfrac{1}{2}.2.3:2+\dfrac{1}{3}.3.4:2+...+\dfrac{1}{20}.20.21:2\)
\(=\dfrac{2}{2}+\dfrac{3}{2}+...+\dfrac{21}{2}\)
\(=\dfrac{2+3+...+21}{2}\)
\(=\dfrac{230}{2}\)
\(=115\)
BT
1
17 tháng 11 2016
B = 1+[1/2 (1+2) 2]/2 +[1/3 (1+2+3) 3]/2 +....+ [1/16 (1+2+3+...+20) 16] /2
B = 1+3/2 + 4/2 +...+ 17/2
B = 1/2 (2+3+4+....+17)
B= 1/2 [(2+7)16]/2
B= 76
Nhớ k cho mình nhé :D
HH
0