Đặt \(A=\frac{3}{10.12}+\frac{3}{12.14}+.....+\frac{3}{48.50}\)
\(A=\frac{3}{2}.\left(\frac{2}{10.12}+\frac{2}{12.14}+......+\frac{2}{48.50}\right)\)
\(A=\frac{3}{2}.\left(\frac{1}{10}-\frac{1}{12}+....+\frac{1}{48}-\frac{1}{50}\right)\)
\(A=\frac{3}{2}.\left(\frac{1}{10}-\frac{1}{50}\right)\)
\(A=\frac{3}{2}.\frac{2}{25}\)
\(A=\frac{3}{25}\)
3/10.12+3/12.14+............+3/48.50
=3/2.(2/10.12+2/12.14+..........+2/48.50)
=3/2(2/10-2/12+2/12-2/14+......+2/48-2/50)
=3/2.(2/10-2/50)
=3/2.4/25
=6/25
=3/2(2/10.12+2/12.14+2/14.16+...+2/48.50)
3/2(1/10-1/12+1/12-1/11+1/14-1/16+...+1/48-1/50)
