A=\(\frac{3}{4}.\frac{8}{9}.\frac{15}{16}.........\frac{899}{900}\)

A=\(\frac{1.3}{2.2}.\frac{2.4}{3.3}.\frac{3.5}{4.4}..........\frac{29.31}{30.30}\)

A=\(\frac{1.2.3.......29}{2.3.4.......30}.\frac{3.4.5........31}{2.3.4.......30}\)

A=\(\frac{1}{30}.\frac{2}{31}=\frac{1}{465}\)

\(A=\dfrac{3}{4}\cdot\dfrac{8}{9}\cdot\dfrac{15}{16}\cdot...\cdot\dfrac{899}{900}\\ =\dfrac{1\cdot3}{2\cdot2}\cdot\dfrac{2\cdot4}{3\cdot3}\cdot\dfrac{3\cdot5}{4\cdot4}\cdot...\cdot\dfrac{29\cdot31}{30\cdot30}\\ =\dfrac{1\cdot2\cdot3\cdot...\cdot29}{2\cdot3\cdot4\cdot...\cdot30}\cdot\dfrac{3\cdot4\cdot5\cdot...\cdot31}{2\cdot3\cdot4\cdot...\cdot30}\\ =\dfrac{1}{30}\cdot\dfrac{31}{2}\\ =\dfrac{31}{60}\)

Vậy ...

\(A=\frac{3}{4}.\frac{8}{9}.\frac{15}{16}.......\frac{899}{900}=\frac{1.3}{2.2}.\frac{2.4}{3.3}.\frac{3.5}{4.4}......\frac{29.31}{30.30}=\frac{1.2.3.....29}{2.3.4......30}.\frac{3.4.5......31}{2.3.4......30}\)

\(=\frac{1}{30}.\frac{31}{2}=\frac{31}{60}\)

chứng tỏ rằng 1/5 + 1/6 + 1/7 + .....+ 1/17 < 2 

\(A=\frac{3}{4}.\frac{8}{9}.\frac{15}{16}......\frac{99}{100}\)

\(=\frac{1.3}{2.2}.\frac{2.4}{3.3}.\frac{3.5}{4.4}......\frac{9.11}{10.10}\)

\(=\frac{\left(1.2.3...9\right).\left(3.4.5...11\right)}{\left(2.3.4...10\right).\left(2.3.4...10\right)}\)

\(=\frac{1}{10}.\frac{11}{2}=\frac{11}{20}\)

bó tay

A=3/4.8/9 .15/16.....899/900

A=1.3/2^2 .   2.4 /3^2  .   3.5/4^2 ....... 29.31 / 30^2

A= 1.2.3.....29 / 2.3.4....30   .   3.4.5...31 / 2.3.4....30

A=1/30 . 31/2 

A= 31/60

Nhớ k nha

A=\(\frac{31}{60}\)

A=\(\frac{31}{60}\)

A=1.3/2²x2.4/3²x....x29.31/30²

A=1.3.2.4.3.5......29.31/2².3².....30²

A=(1.2.3.....29).(3.4.5.... 31)/(2.3....30)(2.3.4....30)

A=1.31/30.2

A=31/60

A=\(\frac{1\times3}{2\times2}\times\frac{2\times4}{3\times3}\times\frac{3\times5}{4\times4}...\times\frac{29\times31}{30\times30}\)

A=\(\frac{1\times2\times3\times...\times29}{2\times3\times4\times...\times30}\times\frac{3\times4\times5\times...\times31}{2\times3\times4\times...\times30}\)

A=\(\frac{1}{30}\times\frac{31}{2}\)

A=\(\frac{31}{60}\)

Tớ cũng giống Như bạn ấy