105/210 chính xác 100%

\(\frac{3.5.7}{21.10}=\frac{3.5.7}{7.3.5.2}=\frac{1}{2}\) vậy giá trj biểu thức là \(\frac{1}{2}\)

3*5*7=105

21*10=210

3*5*7/21*10=105/210

1/2 đó k mình nha

\(\frac{3\cdot5\cdot7}{21\cdot10}=\frac{21\cdot5}{21\cdot10}=\frac{1}{2}\)

tk cho mk nhé.

\(A=\frac{1}{3}\)

\(\frac{3.5.7+6.10.14+9.15.21}{5.7.9+10.14.18+15.21.27}\)

= \(\frac{3.5.7+3.2.5.2.7.2+3.3.5.3.7.21}{5.7.9+5.2.7.2.9.2+5.3.7.3.9.3}\)

 = \(\frac{3.5.7+3.5.7.2.2.2+3.5.7.3.3.3}{5.7.9+5.7.9.2.2.2+5.7.9.3.3.3}\)

= \(\frac{3.5.7+3.5.7.8+3.5.7.27}{5.7.9+5.7.9.8+5.7.9.27}\)

= \(\frac{3.5.7.\left(1+8+27\right)}{5.7.9.\left(1+8+27\right)}\)

= \(\frac{3.5.7.36}{5.7.9.36}\)

= \(\frac{1}{3}\)

3.5.7 là sao

đáp án là 277.1937

277.1937

giúp mình với ạ

\(\dfrac{3}{1\cdot3\cdot5}+\dfrac{3}{3\cdot5\cdot7}+\dfrac{3}{5\cdot7\cdot9}+\cdot\cdot\cdot+\dfrac{3}{37\cdot39\cdot41}\)

\(=\dfrac{3}{4}\left(\dfrac{4}{1\cdot3\cdot5}+\dfrac{4}{3\cdot5\cdot7}+\dfrac{4}{5\cdot7\cdot9}+\cdot\cdot\cdot+\dfrac{4}{37\cdot39\cdot41}\right)\)

\(=\dfrac{3}{4}\left(\dfrac{1}{1\cdot3}-\dfrac{1}{3\cdot5}+\dfrac{1}{3\cdot5}-\dfrac{1}{5\cdot7}+\dfrac{1}{5\cdot7}-\dfrac{1}{7\cdot9}+\cdot\cdot\cdot+\dfrac{1}{37\cdot39}-\dfrac{1}{39\cdot41}\right)\)

\(=\dfrac{3}{4}\left(\dfrac{1}{3}-\dfrac{1}{39\cdot41}\right)\)

\(=\dfrac{3}{4}\cdot\dfrac{532}{1599}=\dfrac{133}{533}\)

#Ayumu