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Sai rồi, để tôi sửa lại:

\(\frac{3}{2^2}.\frac{8}{3^2}.....\frac{899}{30^2}=\frac{1.3}{2.2}.\frac{2.4}{3.3}.....\frac{29.31}{30.30}\)

\(=\frac{1.2.3.....31}{2.3.4.....30}.\frac{3.4.5....29}{2.3.4....30}=31.\frac{1}{60}=\frac{31}{60}\)

dễ quá >>>>>> 31/60

\(\dfrac{3}{2^2}.\dfrac{8}{3^2}.\dfrac{15}{4^2}.....\dfrac{899}{30^2}\)

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

= \(\dfrac{1.3.2.4.3.5.....29.31}{2.2.3.3.4.4.....30.30}\)

=\(\dfrac{\left(1.2.3.....29\right).\left(3.4.5......31\right)}{\left(2.3.4......30\right).\left(2.3.4.....30\right)}\) 

= \(\dfrac{1.31}{2.30}\) 

= \(\dfrac{31}{60}\)

Ta có: \(\dfrac{3}{2^2}\cdot\dfrac{8}{3^2}\cdot\dfrac{15}{4^2}\cdot...\cdot\dfrac{899}{30^2}\)

\(=\dfrac{1\cdot3}{2\cdot2}\cdot\dfrac{2\cdot2^2}{3\cdot3}\cdot\dfrac{3\cdot5}{4\cdot4}\cdot...\cdot\dfrac{29\cdot31}{30\cdot30}\)

\(=\dfrac{\left(1\cdot2\cdot3\cdot...\cdot29\right)\cdot\left(3\cdot4\cdot5\cdot...\cdot31\right)}{\left(2\cdot3\cdot4\cdot...\cdot30\right)\left(2\cdot3\cdot4\cdot...\cdot30\right)}\)

\(=\dfrac{1\cdot31}{2\cdot30}=\dfrac{31}{60}\)

\(A=\frac{3}{2^2}.\frac{8}{3^2}.\frac{15}{4^2}...\frac{899}{30^2}=\frac{1.3.2.4.3.5...29.31}{2.2.3.3.4.4...30.30}=\frac{\left(2.3...29.30\right).\left(3.4.5...29.31\right)}{\left(2.3...29.30\right).\left(2.3.4...29.30\right)}=\frac{31}{2.30}=\frac{31}{60}\)

Gjngkbb. Mk

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