A = 1.2. + 2.3 + 3.4 + ... + 99.100
3A = 1.2.3 + 2.3.(4-1) + ... + 99.100.(101-98)
3A = 1.2.3 + 2.3.4 - 2.3.1 + ... + 99.100.101 - 99.100.98
3A = 99.100.101
3A = 999900
A = 333300
A=1.2+2.3+3.4+...........+99.100
B=1.3+3.5+5.7+............+97.99
C=1.2.3+2.3.4+.............+98.99.100
Bài tập: Tính tổng
a) A = 1.2+2.3+3.4+...+98.99
b) B = 1.3+3.5+5.7+...+99.101
c) S = 1.4+4.7+7.10+...+2017.2020
d) E= 2.4+4.6+6.8+...+98.100
e) S= 1.2.3+2.3.4+3.4.5+...+98.99.100
f) S= 1.2.3.4+2.3.4.5+3.4.5.6+...+19.20.21.22
a,
1.2+2.3+3.4+...+99.100
b,
1.3+2.4+3.5+...+99.101
c,
1.4+2.5+3.6+...+99.102
d,
1.2.3+2.3.4+3.4.5+...+98.99.100
Tính nhanh
A=1.2+2.3+3.4+...+1999.2000
B=1.1+2.2+3.3+...+1999.1999
C=1.2.3+2.3.4+...+48.48.50
D=1.3+3.5+5.7+...+97.99
Tính:
a,A=1.2+2.3+3.4+......+99.100
b,B=1.3+2.4+3.5+......+99.101
c,C=1.4+2.5+3.6+......+99.102
d,D=1.2.3+2.3.4+3.4.5+.......+98.99.100
Tính nhanh:
a/ 2.4 + 4.6 + 6.8+........ + 18.20
b/ 1.3 + 3.5 + 5.7+.......... 19+20
c/ 1.2.3 + 2.3.4 + 3.4.5 + ........+ 18.19.20
d/ 1.2 + 2.3 + 3.4 + ......... + 99.100
bai 1 : a = 1.2+2.3+3.4+4.5+5.6+............+99.100
1.3+3.5+5.7 +9.11 +..........+2011.2013
1+4+9+16+ ...............+ 9801+10000
a=1.2.3+2.3.4+..........+98.99.100
bai 2 : a ) [ -2008.57+1004.(-86 )]:[32.74+16.(-48)
b) 1+2-3-4+5+6-7-8+9+10-.........................+2006-2007-2008+2009
Tính tổng:
A=1.2.3+2.3.4+3.4.5+...…+99.100.101
B=1.2+3.4+51.6+…+99.100
C=1.3+3.5+5.7+…+97.99
D=1.3.5+3.5.7+…+95.97.99
Tính nhanh
S=1.2+3.4+4.5+............+1999.2000
B=1.1+2.2+3.3+......................+1999.1999
C=1.2.3+2.3.4+.......................+48.49.50
D=1.3+3.5+5.7+7.9+..............+97.99