Question

TÍNH NHANH A=\(\frac{1}{1.2}\) +\(\frac{1}{2.3}\) +\(\frac{1}{3.4}\)+ ......\(\frac{1}{9.10}\)

Answer 1

I'm so sorry!

...\(A=1-\frac{1}{10}=\frac{9}{10}\)

Answer 2

mình học ngu lắm

Answer 3

Dễ ợt.

\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{9.10}\)

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

\(A=\frac{1}{2}-\frac{1}{10}=\frac{4}{10}=\frac{2}{5}\)

Answer 4

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

A =1/1 - 1/10

A =9/10

k mình nha ^ _ ^