\(a,\dfrac{5}{7}x+\dfrac{1}{3}=\dfrac{5}{21}:\dfrac{5}{3}\\ \dfrac{5}{7}x+\dfrac{1}{3}=\dfrac{1}{7}\\ \dfrac{5}{7}x=\dfrac{1}{7}-\dfrac{1}{3}\\ \dfrac{5}{7}x=-\dfrac{4}{21}\\ x=\left(-\dfrac{4}{21}\right):\dfrac{5}{7}\\ x=-\dfrac{4}{15}\\ b,\dfrac{3x-1}{14}=\dfrac{8}{14}\\ 3x-1=8\\ 3x=9\\ x=3\)
\(a,\dfrac{5}{7}.x+\dfrac{1}{3}=\dfrac{5}{21}.\sqrt{\dfrac{25}{9}}\)
\(\dfrac{5}{7}.x+\dfrac{1}{3}=\dfrac{5}{21}.\dfrac{5}{3}\)
\(\dfrac{5}{7}.x+\dfrac{1}{3}=\dfrac{25}{63}\)
\(\dfrac{5}{7}.x=\dfrac{25}{63}-\dfrac{1}{3}\)
\(\dfrac{5}{7}.x=\dfrac{4}{63}\)
\(x=\dfrac{4}{63}:\dfrac{5}{7}\)
\(x=\dfrac{4}{63}.\dfrac{7}{5}\)
\(x=\dfrac{4}{45}\)
\(b,\dfrac{3x-1}{14}=\dfrac{4}{7}\)
\(\dfrac{3x-1}{14}=\dfrac{2.4}{2.7}\)
\(\dfrac{3x-1}{14}=\dfrac{8}{14}\)
\(\Rightarrow3x-1=8\)
\(3x=8+1\)
\(3x=9\)
\(x=9:3\)
\(x=3\)