Question

[nguyễn nhật lệ]

1/2+ 1/6 + 1/12+ 1/20+1/30+ 1/42 = ? 

Answer 1

[Đinh Tuấn Việt]

Ta có: 1/2+1/6+1/12+1/20+1/30+1/42

=1/(1*2)+1/(2*3)+1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)

=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7

=1-1/7

=6/7

Answer 2

[nguyen truong giang]

=1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7

=1/1-1/7

=6/7