Tính tổng:
a,S=1.4+4.7+7.10+...+301.304
b,S=1/1.2.3+1/2.3.4+....+1/98.99.100
chưng tỏ 1/1.2.3 +1/2.3.4 + 1/3.4.5+...+1/98.99.100=4949/19800
CMR: 1/(1.2.3)+1/(2.3.4)+...+1/(98.99.100)=4949/19800
chứng tỏ
1/1.2.3 + 1/2.3.4 + 1/3.4.5 + ... + 1/98.99.100 = 4949/19800
\(B=\frac{1}{1.2.3}+\frac{1}{2.3.4}+.........+\frac{1}{98.99.100}\)
tính:A=\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{98.99.100}\)
Tìm x: \(\frac{1}{1.2.3}+\frac{1}{2.3.4}+..+\frac{1}{98.99.100}-3x=\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+..+\frac{1}{27.28.29.30}\)
B=1.2.3+2.3.4+...+97.98.99+98.99.100
A= 1.2.3 + 2.3.4 + 3.4.5 + ... + 98.99.100
