Ta có: \(E=1\cdot3+2\cdot4+\cdots+96\cdot98\)
\(=1\cdot\left(1+2\right)+2\cdot\left(2+2\right)+\cdots+96\left(96+2\right)\)
\(=\left(1^2+2^2+\cdots+96^2\right)+2\left(1+2+\cdots+96\right)\)
\(=\frac{96\left(96+1\right)\left(2\cdot96+1\right)}{6}+2\cdot\frac{96\cdot97}{2}\)
\(=16\cdot97\cdot193+96\cdot97=308848\)
Tính gia trị biểu thức
a) A=1.2+2.3+3.4+…+9.10
b) B=1.2.3+2.3.4+3.4.5+….+7.8.9+8.9.10
c) C=1.3+3.5+5.7+…+95.97+97.99
d) D=51.53+53.55+…+153.155+155.157
e) E=1.3.5+3.5.7+…+15.17.19 +17.19.21
f) F=2.4+4.6+6.8+…+96.98+98.100
AI LÀM NHANH NHẤT MÌNH TICK CHO
1.3+2.4+3.5+4.6+....+99.101=?
1.3+2.4+3.5+4.6+...+100.102=?
1.3 + 2.4 + 3.5 + 4.6 +.........+ 97.99 + 98.100
tính S=1.3+2.4+3.5+4.6+...+48.50
Tính nhanh :C=1.3-2.4+3.5+4.6+....+7.9-8.10
tính C=1.3+2.4+3.5+4.6+.....+(n-1).(n+1)
Tính tổng sau S= 1.3+2.4+3.5+4.6+....+99.101+100.102
A= \(\frac{1}{2.4}-\frac{1}{3.5}+\frac{1}{4.6}-\frac{1}{5.7}+.....-\frac{1}{97.99}+\frac{1}{96.98}-\frac{1}{97.99}\)
