\(\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+...+\frac{1}{47.48.49.50}\)
\(=\frac{1}{3}\cdot\left(\frac{1}{1.2.3}-\frac{1}{2.3.4}+\frac{1}{2.3.4}-\frac{1}{3.4.5}+...+\frac{1}{47.48.49}-\frac{1}{48.49.50}\right)\)
\(=\frac{1}{3}\cdot\left(\frac{1}{1.2.3}-\frac{1}{48.49.50}\right)\)
\(=\frac{1}{3}\cdot\frac{6533}{39200}=\frac{6533}{117600}\)
\(\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+\frac{1}{3.4.5.6}+......+\frac{1}{47.48.49.50}\)
bằng mấy nhỉ
F=\(\frac{1}{1.2.3.4}\)+\(\frac{1}{2.3.4.5}\)+\(\frac{1}{3.4.5.6}\)+...+\(\frac{1}{47.48.49.50}\)
\(E=\frac{1}{1.2}-\frac{1}{1.2.3}+\frac{1}{2.3}-\frac{1}{2.3.4}+\frac{1}{3.4}-\frac{1}{3.4.5}+....+\frac{1}{99.100}-\frac{1}{99.100.101}\)
\(F=\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+\frac{1}{3.4.5.6}+...+\frac{1}{47.48.49.50}\)
Tính
\(C=1+\frac{1}{\left(-3\right)}+\frac{1}{\left(-3\right)^2}+....+\frac{1}{\left(-3\right)^{2015}}\)
Tính F = 1/1.2.3.4 +1/2.3.4.5+1/3.4.5.6+....+1/47.48.49.50
tính:
\(\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+\frac{1}{3.4.5.6}+...+\frac{1}{97.98.99.100}\)
\(y=\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+...+\frac{1}{27.28.29.30}\)
A=\(\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+......+\frac{1}{7.8.9.10}\)
Tính
a) K =\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+\frac{1}{3.4.5}+...+\frac{1}{2015.2016.2017}\)
b) O = \(\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+\frac{1}{3.4.5.6}+...+\frac{1}{2015.2016.2017.2018}\)
Tính nhanh \(B=\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+...+\frac{1}{n.\left(n+1\right).\left(n+2\right).\left(n+3\right)}\)
