Question

[Đoàn Mạnh Tuấn]

 

4	+	4	+ … +	4	=
6 x 8	8 x 10	126 x 128

Answer 1

[Nguyễn Thị Thương Hoài]

A = \(\dfrac{4}{6\times8}\) + \(\dfrac{4}{8\times10}\) + ......+\(\dfrac{4}{126\times128}\)

A = 2x ( \(\dfrac{2}{6\times8}\) + \(\dfrac{2}{8\times10}\) +......+ \(\dfrac{2}{126\times128}\))

A = 2 x ( \(\dfrac{1}{6}\) - \(\dfrac{1}{8}\) + \(\dfrac{1}{8}\) - \(\dfrac{1}{10}\) + .......+ \(\dfrac{1}{126}\) - \(\dfrac{1}{128}\))

A = 2 x ( \(\dfrac{1}{6}\) - \(\dfrac{1}{128}\))

A = 2 x \(\dfrac{61}{384}\)

A = \(\dfrac{61}{192}\)