Question

1/1.2 .1/2.3 ... .1/999.1000

Answer 1

Đặt A= 1/1.2 + 1/2.3 + 1/3.4+...+ 1/999.1000

=1-1/2+1/2-1/3+1/3-1/4+...+1/999-1/1000

=1-1/1000

=999/1000

Answer 2

\(\dfrac{1}{1.2}+\dfrac{1}{2.3}+.....+\dfrac{1}{999.1000}\)

\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+.....+\dfrac{1}{999}-\dfrac{1}{1000}\)

\(=1-\dfrac{1}{1000}\)

\(=\dfrac{999}{1000}\)