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\(a)\left(-\dfrac{3}{4}\div\dfrac{2}{-3}\right)\times\dfrac{-5}{7}\)
\(=\dfrac{9}{8}\times\dfrac{-5}{7}\)
\(=\dfrac{-45}{56}\)
\(b)\dfrac{-2}{-5}\div\left(\dfrac{7}{-5}\div\dfrac{-3}{2}\right)\)
\(=\dfrac{2}{5}\div\left(\dfrac{7}{-5}\div\dfrac{-3}{2}\right)\)
\(=\dfrac{2}{5}\div\dfrac{14}{15}\)
\(=\dfrac{3}{7}\)
\(A=2^5.5^2-8^2-7=800-64-7=729=27^2\)
\(B=2^3.4^2+3^2.3^2-40=128+81-40=169=13^2\)
\(C=11.2^4+6^2.19+40=176+684+40=900=30^2\)
\(D=4^3+6^3+7^3+2=64+216+343+2=625=25^2\)
\(\dfrac{6}{7}+\dfrac{5}{8}:5-\dfrac{3}{16}.\left(-2\right)^2=\dfrac{6}{7}+\dfrac{5}{8}:5-\dfrac{3}{16}.4=\dfrac{6}{7}+\dfrac{1}{8}-\dfrac{3}{4}=\dfrac{5}{56}\)
\(\dfrac{2}{3}+\dfrac{1}{3}.\left(-\dfrac{4}{9}+\dfrac{5}{6}\right):\dfrac{7}{12}=\dfrac{2}{3}+\dfrac{1}{3}.\dfrac{7}{18}:\dfrac{7}{12}=\dfrac{2}{3}+\dfrac{2}{9}=\dfrac{8}{9}\)