\(M=2a-\dfrac{5b}{a}-3b\)
\(\dfrac{a}{b}=\dfrac{3}{5}\Rightarrow a=\dfrac{3}{5}b\) và \(\dfrac{b}{a}=\dfrac{5}{3}\)
\(\Rightarrow M=2.\dfrac{3}{5}b-5.\dfrac{5}{3}-3b\)
\(\Rightarrow M=\dfrac{6}{5}b-3b-\dfrac{25}{3}\)
\(\Rightarrow M=\left(\dfrac{6}{5}-3\right)b-\dfrac{25}{3}\)
\(\Rightarrow M=\dfrac{-9}{5}b-\dfrac{25}{3}\)