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Ta có:
\(\frac{3}{4}.\frac{8}{9}.\frac{15}{16}.\frac{24}{25}.\frac{35}{36}.\frac{48}{49}=\frac{1.3}{2.2}+\frac{2.4}{3.3}+\frac{3.5}{4.4}+\frac{4.6}{5.5}+\frac{5.7}{6.6}+\frac{6.8}{7.7}=\frac{1.2.3.4.5.6}{2.3.4.5.6.7}.\frac{3.4.5.6.7.8}{2.3.4.5.6.7}=\frac{1}{7}.\frac{8}{2}=\frac{4}{7}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(\frac{-6}{35}.\frac{-49}{60}=\frac{\left(-6\right).\left(-49\right)}{35.60}=\frac{\left(-6\right).\left(-7\right).\left(-7\right)}{\left(-5\right).\left(-7\right).\left(-6\right).\left(-10\right)}=\frac{-7}{\left(-5\right).\left(-10\right)}=\frac{-7}{50}\)
b) \(\frac{-16}{25}.\frac{-5}{24}=\frac{\left(-16\right).\left(-5\right)}{25.24}=\frac{\left(-8\right).2.\left(-5\right)}{\left(-5\right).\left(-5\right).\left(-8\right).\left(-3\right)}=\frac{2}{\left(-5\right).\left(-3\right)}=\frac{2}{15}\)
c) \(\frac{15}{-17}.\frac{5}{18}=\frac{15.5}{\left(-17\right).18}=\frac{5.3.5}{\left(-17\right).3.6}=\frac{5.5}{\left(-17\right).6}=\frac{25}{-102}\)
a) \(\frac{-6}{35}\cdot\frac{-49}{60}\)
\(=\frac{\left(-6\right)\cdot\left(-49\right)}{35\cdot60}\)
\(=\frac{294}{2100}=\frac{7}{50}\)
b)\(\frac{-16}{25}\cdot\frac{-5}{24}\)
\(=\frac{\left(-16\right)\cdot\left(-5\right)}{25\cdot24}\)
\(=\frac{80}{600}=\frac{2}{15}\)
c)\(\frac{15}{-17}\cdot\frac{5}{18}\)
\(=\frac{15\cdot5}{\left(-17\right)\cdot18}\)
\(=\frac{75}{-306}=\frac{25}{-102}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
mình biết đáp án là : \(\frac{9}{16}\)thôi,còn cách giải thì mình không chắc chắn nên không viết ra
\(\frac{3.2.4.3.5.4.6.5.7.6.8.7.9}{4.3.3.4.4.5.5.6.6.7.7.8.8}\)= \(\frac{9}{16}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(A=\frac{8}{9}.\ \frac{15}{16}.\ \frac{24}{25}.\ \frac{35}{36}.\ \frac{48}{49}.\ \frac{63}{64}\)
\(A=\frac{2.4}{3^2}.\ \frac{3.5}{4^2}.\ \frac{4.6}{5^2}.\ \frac{5.7}{6^2}.\ \frac{6.8}{7^2}.\ \frac{7.9}{8^2}\)
\(A=\frac{2.3.4^2.5^2.6^2.7^2.8.9}{3^2.4^2.5^2.6^2.7^2.8^2}\)
\(A=\frac{2.9}{3.8}\)
\(A=\frac{3}{4}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{3}{4}.\frac{8}{9}.\frac{15}{16}.\frac{24}{25}...\frac{63}{64}\)
\(=\frac{1.3}{2.2}.\frac{2.4}{3.3}.\frac{3.5}{4.4}.\frac{4.6}{5.5}...\frac{7.9}{8.8}\)
\(=\frac{1.3.2.4.3.5.4.6...7.9}{2.2.3.3.4.4.5.5...8.8}\)
\(=\frac{1.9}{2.8}=\frac{9}{16}\)
\(1,8\cdot1\frac{1}{24}-\left(25-24\frac{17}{49}\right):\frac{16}{49}\)
\(=1,8\cdot\frac{25}{24}-\left(25-24+\frac{17}{49}\right):\frac{16}{49}\)
\(=\frac{15}{8}-\frac{66}{49}:\frac{16}{49}\)
\(=\frac{15}{8}-\frac{33}{8}=\frac{-9}{4}\)