Question

vì sao \(\frac{2}{n\left(n+1\right)}=\frac{1}{n\left(n+1\right)}-\frac{1}{\left(n+1\right)\left(n+2\right)}\)

Answer 1

\(\frac{1}{n\left(n+1\right)}-\frac{1}{\left(n+1\right)\left(n+2\right)}=\frac{n+2}{n\left(n+1\right)\left(n+2\right)}-\frac{n}{n\left(n+1\right)\left(n+2\right)}=\frac{n+2-n}{n\left(n+1\right)\left(n+2\right)}\)=\(\frac{2}{n\left(n+1\right)\left(n+2\right)}\)

Mình nghĩ đề sai

Answer 2

thiếu 2/n*(n+1)*(n+2)=1/n*(n+1)-1/(n+1)*(n+2) nhé tui làm mò thôi ai ngờ ra công thức 

VD:2/2*3*4=1/2*3-1/3*4=1/6-1/12=1/12

mà 2/2*3*4=2*24=1/12