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a) \(\frac{37}{25}+\frac{11}{21}-\frac{12}{25}+\frac{10}{21}\)
= \(\left(\frac{37}{25}-\frac{12}{25}\right)+\left(\frac{11}{21}+\frac{10}{21}\right)\)
= 1 + 1
= 2
\(\frac{37}{25}+\frac{11}{21}-\frac{12}{25}+\frac{10}{21}\)
=\(\left(\frac{37}{25}-\frac{12}{25}\right)+\left(\frac{11}{21}+\frac{11}{21}\right)\)
= 1 + 1 = 2 .

a) \(11^{21}>9^{21}=\left(3^2\right)^{21}=3^{2.21}=3^{42}>3^{39}\)
b) \(5^{36}=\left(5^3\right)^{12}=125^{12}\)
\(11^{24}=\left(11^2\right)^{12}=121^{12}\)
Ta có: \(125>121\Rightarrow125^{12}>121^{12}\Rightarrow5^{36}>11^{24}\)
c) \(21^{15}=\left(3.7\right)^{15}=3^{15}.7^{15}\)
\(27^5.49^8=\left(3^3\right)^5.\left(7^2\right)^8=3^{15}.7^{16}\)
Ta có: \(7^{15}< 7^{16}\Rightarrow3^{15}.7^{15}< 3^{15}.7^{16}\Rightarrow2^{15}< 27^5.49^8\)
d) \(3^{99}=\left(3^3\right)^{33}=27^{33}>11^{21}\)

\(14.\frac{5}{21}=\frac{14}{1}.\frac{5}{21}=\frac{14.5}{21}=\frac{10}{3}\)
\(\frac{5}{21}.14=\frac{5.14}{21.1}=\frac{5.2}{3.1}=\frac{10}{3}\)
\(10:\frac{5}{3}=10.\frac{3}{5}=\frac{10.3}{5}=2.3=6\)
\(\frac{5}{3}:10=\frac{5}{3}.\frac{1}{10}=\frac{5}{3.10}=\frac{1}{6}\)

Tớ nghĩ là ý B , cách làm là : \(1344\div63=21\frac{1}{3}\)
Nhưng nếu đúng thì k mik nha

\(\frac{5}{9}\) . \(\frac{a}{b}\) - \(\frac{11}{21}\) = \(\frac{4}{21}\)
\(\frac{5}{9}\) . \(\frac{a}{b}\) = \(\frac{4}{21}\) + \(\frac{11}{21}\)
\(\frac{5}{9}\) . \(\frac{a}{b}\) = \(\frac{5}{7}\)
\(\frac{a}{b}\) = \(\frac{5}{7}\) : \(\frac{5}{9}\)
\(\frac{a}{b}\) = \(\frac{9}{7}\)
Vậy \(\frac{a}{b}\) = \(\frac{9}{7}\)
5/9 x a/b-11/21=4/21
<=> 5/9 x a/b=4/21+11/21
<=> 5/9 x a/b = 21/21=1
<=> a/b = 1 : 5/9
<=> a/b=9/5
Vậy a/b=9/5
cứu tao hiếu ơi