Question

[Đào Minh Quang]

Tính \(A=\frac{1}{3\cdot7}+\frac{1}{7\cdot11}+\frac{1}{11\cdot15}+...+\frac{1}{91\cdot95}\)

Answer 1

[qwedsa123]

A=1/3.7+1/7.11+1/11.15+...+1/91.95

=>4A=4/3.7+4/7.11+4/11.15+...+4/91.95

    4A=1/3-1/7+1/7-1/11+1/11-1/15+...1/91-1/95

    4A=1/3-1/95

    4A=92/285

      A=92/285:4

      A=23/285

Answer 2

[Đào Minh Quang]

Thank