Question

1/4.5 + 1/5.6 + 1/6.7 + ....+ 1/39.40

Answer 1

thoyy,tui xin chịu ạ

Answer 2

=1/4+1/5-1/5+...-1/39+1/40

=1/4+1/19

=.....(tự tính nka)

Answer 3

\(\dfrac{1}{4.5}+\dfrac{1}{5.6}+...+\dfrac{1}{39.40}\)

\(=\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+...+\dfrac{1}{39}-\dfrac{1}{40}\)

\(=\dfrac{1}{4}-\dfrac{1}{40}\)

\(=\dfrac{9}{40}\)