a: \(=\dfrac{21}{25}\cdot\dfrac{11}{9}\cdot\dfrac{5}{7}=\dfrac{1}{3}\cdot11\cdot\dfrac{1}{5}=\dfrac{11}{15}\)
b: \(=\dfrac{5}{23}\left(\dfrac{17}{26}+\dfrac{9}{26}\right)=\dfrac{5}{23}\)
c: \(=\dfrac{7}{19}\cdot\dfrac{5}{13}+\dfrac{7}{19}\cdot\dfrac{8}{13}-3\cdot\dfrac{7}{19}=\dfrac{7}{19}\cdot\left(-2\right)=-\dfrac{14}{19}\)
\(a,=\dfrac{21.11.5}{25.9.7}=\dfrac{3.11.1}{5.9.1}=\dfrac{33}{45}=\dfrac{11}{15}\)
\(b,=\dfrac{5}{23}.\left(\dfrac{17}{26}+\dfrac{9}{26}\right)\)
\(=\dfrac{5}{23}.1=\dfrac{5}{23}\)
\(c,=\dfrac{7}{19}.\dfrac{5}{13}+\dfrac{7}{19}.\dfrac{8}{13}-3.\dfrac{7}{19}\)
\(=\dfrac{7}{19}.\left(\dfrac{5}{13}+\dfrac{8}{13}-3\right)\)
\(=\dfrac{7}{19}.\left(-2\right)=\dfrac{-14}{19}\)
