\[{{}_{2}\phi_{1}}\left({aq,b/q\atop c};q,z\right)-{{}_{2}\phi_{1}}\left({a,b%
\atop c};q,z\right)=az\frac{(1-b/(aq))}{1-c}{{}_{2}\phi_{1}}\left({aq,b\atop cq%
};q,z\right),\]