Question

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

Answer 1

S= 1/1 - 1/2 + 1/2 - 1/3 +...+ 1/n - 1/(n+1) 
=> S= 1/1 - 1/(n+1) 
=> S= n/(n+1)

Answer 2

bai nay trong may sach tham khao nhieu lam

Answer 3

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

=1-1/(n+1)

=n/(n+1)