\(\frac{1.3.5+2.6.10+4.12.20+7.21.35}{1.5.7+2.10.14+4.20.28+7.35.49}\)

\(=\frac{1.3.5\left(1+2+4+7\right)}{1.5.7\left(1+2+7+7\right)}=\frac{1.3.5}{1.5.7}=\frac{15}{35}=\frac{3}{7}\)

\(\frac{1\cdot3\cdot5+2\cdot6\cdot10+4\cdot12\cdot20+7\cdot21\cdot35}{1\cdot5\cdot7+2\cdot10\cdot14+4\cdot20\cdot28+7\cdot35\cdot49}\)

\(=\)\(\frac{1\cdot3\cdot5\cdot\left(1+2+4+7\right)}{1\cdot5\cdot7\cdot\left(1+2+7+7\right)}\)

\(=\frac{1\cdot3\cdot5}{1\cdot5\cdot7}\)\(=\frac{15}{35}=\frac{3}{7}\)

bn vội quá viết nhầm lun kìa 

hj hj chúc bn làm bài tốt nha

a . 24/50 < 51/100                         b . 2003/2013 < 2004/2014             c . 2121/3131 = 21212121/31313131                                                          

\(\dfrac{20}{35}\text{=}\dfrac{4}{7}\)

\(\dfrac{5}{15}\text{=}\dfrac{1}{3}\)

\(\dfrac{12}{21}\text{=}\dfrac{4}{7}\)

\(\dfrac{8}{10}\text{=}\dfrac{4}{5}\)

\(\dfrac{20}{30}\text{=}\dfrac{2}{3}\)

\(\Rightarrow\left(\dfrac{20}{35}\text{=}\dfrac{12}{21}\text{=}\dfrac{4}{7}\right);\left(\dfrac{20}{30}\text{=}\dfrac{2}{3}\right).\)

4/7 = 12/21 = 20/35

HT

20/35=12/21=4/7
2/3=20/30