Đặt S= 1.2 + 2.3 + 3.4 + ...+ 99.100
3S = 1.2.3+2.3.3+3.4.3+...+98.99.3+99.100.3
3S= 1.2.3+2.3(4-1)+3.4(5-2)+...+98.99(100-97)+99.100(101-98)
3S= 1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...-97.98.99+99.100.101-98.99.100
3S = 99.100.101 3S = 3.33.100.101
S=33.100.101= 333300
Áp dụng tính tổng : S=1.2+2.3+4.5+...+99.100
Tính nhanh:
1.2+2.3+3.4+...+99.100
Tính nhanh: A= \(\dfrac{2022}{1.2}+\dfrac{2022}{2.3}+\dfrac{2022}{3.4}+...+\dfrac{2022}{2021.2022}\)
1/1.2+1/2.3+1/3.4+...+1/x.(x+1)=2022/2021
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Tính nhanh:
1.2+3.4+4.5+...+29.30
Nhanh nhé các bạn
tinh:
a,A=1+2+3+........+2015
b,B=1+2+5+.........+1017
c,C=2+4+6+..........+2014
d,D=1+4+7+...........+2008
e,E=1.2+2.3+3.4+................1001+1002
tinh:
a,A=1+2+3+........+2015
b,B=1+2+5+.........+1017
c,C=2+4+6+..........+2014
d,D=1+4+7+...........+2008
e,E=1.2+2.3+3.4+................1001+1002
tinh:
a,A=1+2+3+........+2015
b,B=1+2+5+.........+1017
c,C=2+4+6+..........+2014
d,D=1+4+7+...........+2008
e,E=1.2+2.3+3.4+................1001+1002
tinh:
a,A=1+2+3+........+2015
b,B=1+2+5+.........+1017
c,C=2+4+6+..........+2014
d,D=1+4+7+...........+2008
e,E=1.2+2.3+3.4+................1001+1002