\(\frac{1}{11×14}+\frac{1}{14×17}+\frac{1}{17×20}+\frac{1}{20×23}+\frac{1}{23×26}\)
\(=\frac{1}{3}×\left(\frac{3}{11×14}+\frac{3}{14×17}+\frac{3}{17×20}+\frac{3}{20×23}+\frac{3}{23×26}\right)\)
\(=\frac{1}{3}×\left(\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{17}+...+\frac{1}{23}-\frac{1}{26}\right)\)
\(=\frac{1}{3}×\left(\frac{1}{11}-\frac{1}{26}\right)\)
\(=\frac{1}{3}×\frac{15}{286}\)
\(=\frac{5}{286}\)
\(\frac{1}{11\times14}+\frac{1}{14\times17}+\frac{1}{17\times20}+\frac{1}{20\times23}+\frac{1}{23\times26}\)
\(=\frac{1}{3}\times\left(\frac{1}{11\times14}+\frac{1}{14\times17}+\frac{1}{17\times20}+\frac{1}{20\times23}+\frac{1}{23\times26}\right)\)
\(=\frac{1}{3}\times\left(\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{17}+\frac{1}{17}-\frac{1}{20}+\frac{1}{20}-\frac{1}{23}+\frac{1}{23}-\frac{1}{26}\right)\)
\(=\frac{1}{3}\times\left(\frac{1}{11}-\frac{1}{26}\right)\)
= 5/286
Đặt biểu thức trên là A. Ta có :
3A = \(\frac{3}{11x14}+\frac{3}{14x17}+\frac{3}{17x20}+\frac{3}{20x23}+\frac{3}{23x26}\)
3A = \(\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{17}+\frac{1}{17}-\frac{1}{20}+\frac{1}{23}-\frac{1}{26}\)
3A = \(\frac{1}{11}-\frac{1}{26}=\frac{15}{286}\)
A = \(\frac{15}{286}:3=\frac{5}{286}\)
Vậy A = \(\frac{15}{286}\)
=1/11+1/14+1/17+1/20+1/23x(14+17+20+23+26)
=1/11+1/14+1/17+1/20+1/23x100
=(1/11+14+17+20+23)x100
=1/85x100
=100/85 hay 1 và 15/85
đúng thì bn k giùm mk nha
Ta có 1/3x(3/11x14+3/14x17+3/17x20+3/20x23+3/23x26)
=1/3x(1/11-1/14+1/14-17+...+1/23-1/26)
=1/3x(1/11-1/26)
=1/3x15/286
=5/286
