A = 1.2.3 + 2.3.4 + 3.4.5 + ... + 99.100.101
4A = 4.(1.2.3 + 2.3.4 + 3.4.5 + ... + 99.100.101)
= 1.2.3.(4-0) + 2.3.4.(5-1) + 3.4.5.(6-2) + ... + 99.100.101.(102-98)
= 1.2.3.4 - 1.2.3.4 + 2.3.4.5 - 2.3.4.5 + 3.4.5.6 - 3.4.5.6 + ... + 98.99.100.101 - 98.99.100.101 + 99.100.101.102
4A = 99.100.101.102
A = 99.100.101.102 : 4
A = 25497450
Tính: 1/1.2.3+1/2.3.4+1/3.4.5+...+1/99.100.101
Tính \(A=\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+.....+\frac{1}{99.100.101}\)
Tính:
f) F= 1.2+2.3+3.4+...+n(n+1)
g) G= 1.2.3+2.3.4+3.4.5+...+99.100.101
h) H= 1.2.3+2.3.4+3.4.5+...+n(n+1)(n+2)
i) I= 1.3+2.4+3.5+...+99.100
j) J= 1.4+2.5+3.6+...+99.102
Tính
\(A=\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{99.100.101}\)
Tính : A=1.2.3+2.3.4+3.4.5+......+99.100.101
Ai vừa thi HSG 7 thành phố cho xin cái đề
tinh A=1/1.2.3+1/2.3.4+....+1/99.100.101
Tính
A = \(\frac{1}{1.2.3}-\frac{1}{2.3.4}-.......-\frac{1}{99.100.101}\)
Tính S=1.2.3+2.3.4+3.4.5+...+97.98.99
tinh
1/1.2.3+1/2.3.4+....+1/99.100.101
