Đặt \(D=\frac{1}{2.4}+\frac{1}{4.6}+...+\frac{1}{98.100}\)
=>\(2D=\frac{2}{2.4}+\frac{2}{4.6}+...+\frac{2}{98.100}\)
=>\(2D=\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+...+\frac{1}{98}-\frac{1}{100}\)
=>\(2D=\frac{1}{2}-\frac{1}{100}\)
=>\(2D=\frac{49}{100}\)
=>\(D=\frac{49}{50}\)