\(a)\) \(A=\frac{5\left(2^2.3^2\right)^9.\left(2^2\right)^6-2\left(2^2.3\right)^{14}.3^4}{5.2^{28}.3^{18}-7.2^{29}.3^{18}}\)

\(A=\frac{2^{30}.3^{18}.5-2^{29}.3^{18}}{2^{28}.3^{18}.5-2^{29}.3^{18}.7}\)

\(A=\frac{2^{29}.3^{18}\left(2.5-1\right)}{2^{28}.3^{18}\left(5-2.7\right)}\)

\(A=\frac{2\left(10-1\right)}{5-14}\)

\(A=\frac{2.9}{-9}\)

\(A=-2\)

Vậy \(A=-2\)

\(b)\) \(B=81.\left[\frac{12-\frac{12}{7}-\frac{12}{289}-\frac{12}{85}}{4-\frac{4}{7}-\frac{4}{289}-\frac{4}{85}}:\frac{5+\frac{5}{13}+\frac{5}{169}+\frac{5}{91}}{6+\frac{6}{13}+\frac{6}{169}+\frac{6}{91}}\right].\frac{158158158}{711711711}\)

\(B=81.\left[\frac{12\left(1-\frac{1}{7}-\frac{1}{289}-\frac{1}{85}\right)}{4\left(1-\frac{1}{7}-\frac{1}{289}-\frac{1}{85}\right)}:\frac{5\left(1+\frac{1}{13}+\frac{1}{169}+\frac{1}{91}\right)}{6\left(1+\frac{1}{13}+\frac{1}{169}+\frac{1}{91}\right)}\right].\frac{158158158}{711711711}\)

\(B=81.\left[\frac{12}{4}:\frac{5}{6}\right].\frac{2}{9}\)

\(B=81.\frac{18}{5}.\frac{2}{9}\)

\(B=\frac{324}{5}\)

Vậy \(B=\frac{324}{5}\)

Chúc bạn học tốt ~ ( mỏi tay qué >_< ) 

nhìn cái đề ớn quá

đúng là ngu như bây

A = \(\frac{5.\left(2^2.3^2\right)^6.\left(2^2\right)^6-2\left(2^2.3\right)^{14}.3^4}{5.2^{28}.3^{18}-7.2^{29}.3^{18}}\)

   = \(\frac{5.2^{18}.3^{18}.2^{12}-2.2^{28}.3^{14}.3^4}{5.2^{28}.3^{18}-7.2.2^{28}.3^{18}}\)

   = \(\frac{5.2^{29}.2.3^{18}-2^{29}.3^{18}}{\left(5-14\right).2^{28}.3^{18}}\)

   = \(\frac{\left(10-1\right).2^{29}.3^{18}}{\left(5-14\right).2^{28}.3^{18}}\)

  = \(\frac{9.2}{-9}\)

  = \(-2\)

Cái này là ra -2

\(A=\frac{5\cdot\left(2^2\cdot3^2\right)^9\cdot\left(2^2\right)^6-2\left(2^2\cdot3\right)^{14}\cdot3^4}{5\cdot2^{28}\cdot3^{18}-7\cdot2^{29}\cdot3^{18}}\)

\(\Rightarrow A=\frac{5\cdot2^{18}\cdot3^{18}\cdot2^{12}-2\cdot2^{28}\cdot3^{14}\cdot3^4}{5\cdot2^{28}\cdot3^{18}-7\cdot2^{28}\cdot2\cdot3^{18}}\)

\(\Rightarrow A=\frac{5\cdot2^{30}\cdot3^{18}-2\cdot2^{28}\cdot3^{18}}{5\cdot2^{28}\cdot3^{18}-14\cdot2^{28}\cdot3^{18}}\)

\(\Rightarrow A=\frac{5\cdot2^{28}\cdot2^2\cdot3^{18}-2\cdot2^{28}\cdot3^{18}}{5\cdot2^{28}\cdot3^{18}-14\cdot2^{28}\cdot3^{18}}\)

\(\Rightarrow A=\frac{20\cdot2^{28}\cdot3^{18}-2\cdot2^{28}\cdot3^{18}}{5\cdot2^{28}\cdot3^{18}-14\cdot2^{28}\cdot3^{18}}\)

\(\Rightarrow A=\frac{2^{28}\cdot3^{18}\cdot\left(20-2\right)}{2^{28}\cdot3^{18}\left(5-14\right)}\)

\(\Rightarrow A=\frac{18}{-9}=-2\)

A = -2 nhé , 

gợi ý các bạn chọn (k) đúng cho mình.

\(A=\frac{5.\left(2^2.3^2\right)^9.\left(2^2\right)^6-2.\left(2^2.3\right)^{14}.3^4}{5.2^{28}.3^{18}-7.2^{29}.3^{18}}\)

\(=\frac{5.2^{18}.3^{18}.2^{12}-2.2^{28}.3^{14}.3^4}{2^{28}.3^{18}.\left(5-7.2\right)}\)\(=\frac{5.2^{30}.3^{18}-2^{29}.3^{18}}{2^{28}.3^{18}.\left(5-14\right)}\)

\(=\frac{2^{29}.3^{18}.\left(5.2-1\right)}{2^{28}.3^{18}.\left(-9\right)}=\frac{2.9}{-9}=-2\)

Vậy A=-2

=\(\frac{5.2^{18}.3^{18}.2^{12}-2.2^{28}.3^{14}.3^4}{5.2^{28}.3^{18}-7.2^{29}.3^{18}}\)

=\(\frac{2^{29}\left(5.3^{18}-3^{18}\right)}{2^{28}\left(5.3^{18}-3^{18}\right).7}\)

=\(\frac{2}{7}\)