a: \(=\dfrac{1}{280}-\dfrac{1}{70}=\dfrac{1}{280}-\dfrac{4}{280}=-\dfrac{3}{280}\)
b: \(=\dfrac{200}{37}\left(\dfrac{85}{26}-\dfrac{59}{26}\right)=\dfrac{200}{37}\)
c: \(=2+\dfrac{2}{2+\dfrac{2}{2+\dfrac{2}{\dfrac{5}{2}}}}=2+\dfrac{2}{2+\dfrac{2}{2+\dfrac{4}{5}}}=2+\dfrac{2}{2+\dfrac{5}{7}}\)
\(=2+2:\dfrac{19}{7}=2+\dfrac{14}{19}=\dfrac{38+14}{19}=\dfrac{52}{19}\)