a: \(=\dfrac{11}{21}\left(\dfrac{7}{4}+\dfrac{5}{4}\right)=\dfrac{11}{21}\cdot3=\dfrac{11}{7}\)
b: \(=1\cdot\dfrac{2}{2}\cdot\dfrac{3}{3}\cdot\dfrac{4}{4}\cdot\dfrac{5}{5}\cdot\dfrac{6}{6}\cdot\dfrac{7}{7}\cdot\dfrac{8}{9}\cdot\dfrac{1}{9}=\dfrac{1}{9}\)
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