Question

Tính tổng

\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+.....+\frac{1}{n\left(n+1\right)}\)

Answer 1

=1-1/2+1/2-1/3+1/3-1/4+.....+1/n-1/n+1

=1-1/n+1

=n/n+1

Answer 2

Ta có : 1/ 1.2 + 1/ 2.3 + 1/ 3.4 + ... + 1/ n.( n + 1 ) .

= 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ..... + 1/n - 1/ n+1 .

= 1 - 1/ n + 1 .

= n+1 / n+1 - 1/ n+1 .

= n/ n+1 .

Đáp sô : n/ n+1

Answer 3

hộ mình cái nha

Answer 4

1/1.2 + 1/2.3 + 1/3.4 + ... + 1/n.(n+1)

=1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/n - 1/n+1

=1 - 1/n+1

= n+1/n+1 - 1/ n+1

=n/n+1