Question

 

1/2*3+1/3*4+1/4*5..............1/9*10

Answer 1

\(\frac{1}{2x3}+\frac{1}{3x4}+...+\frac{1}{9x10}\)

\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)

\(=\frac{1}{2}-\frac{1}{10}\)

\(=\frac{2}{5}\)

Answer 2

đặt A=1/2*3+1/3*4+1/4*5..............1/9*10

\(A=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)

\(=\frac{1}{2}-\frac{1}{10}\)

\(=\frac{4}{10}=\frac{2}{5}\)

Answer 3

1/7*10 đúng không các bạn

Answer 4

\(\frac{1}{2x3}+\frac{1}{3x4}+...+\frac{1}{9x10}=\frac{1}{1}-\frac{1}{2}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}=1-\frac{1}{10}=\frac{9}{10}\)

Answer 5

\(\frac{1}{2x3}+\frac{1}{3x4}+...+\frac{1}{9x10}=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}=\frac{1}{2}-\frac{1}{10}=\frac{5}{10}-\frac{1}{10}=\frac{4}{10}=\frac{2}{5}\)

cái kia nhầm nhé

Answer 6

1/2.3 + 1/3.4 +.....+ 1/9.10

= 1/2 - 1/3 + 1/3 - 1/4 +......+ 1/9 - 1/10

= 1/2 - 1/10

=4/10 = 2/5