A=1.2+2.3+3.4+........+98.99
3A=1.2.3+2.3.3+3.4.3+........+98.99.3
3A=1.2.3+2.3.(4 -1) +3.4.(5 -2)+........+98.99.(100 -97)
3A=1.2.3+2.3.4 -1.2.3 +3.4.5 -2.3.4 +........+98.99.100 -97.98.99
3A=98.99.100
===>A=(98.99.100)/3
1.2+2.3+3.4+4.5+...+98.99
1.2+2.3+3.4+4.5+...+98.99+99.100=?
1.2+2.3+3.4+4.5+.....+97.98+98.99+99.100
tính A=1.2+2.3+3.4+4.5+.........................+98.99+99.100
1.2+2.3+3.4+4.5+....+98.99
Tính tổng:
A=1.2+2.3+3.4+4.5+5.6+.........+98.99+99.100
Tính tổng
a) 9+99+999+...+999999
b) 1+11+111+...+1111111
c)1.2 + 2.3+3.4+4.5+...+98.99
d) 1.3.5 + 3.5.7+5.7.9+...+95.97.99
tinh tong A và B biết:A=1.2+2.3+3.4+4.5+5.6+...+98.99;B=1^2+2^2-3^2+4^2+....+98^2
Tính nhanh :
\(\frac{2}{1.2}+\frac{2}{2.3}+\frac{2}{3.4}+\frac{2}{4.5}+\frac{2}{98.99}+\frac{2}{99.100}\)
