Thevenin's theorem/ Norton's Theorem

Thevenin's theorem/ Norton's theorem is another method used for circuit analysis and simplification. It involves converting circuit sources and impedances to a thevenin equivalent. The picture below shows the Thevenin's and Norton's equivalent circuit of the original circuit. No current flows in ab because it represents an open circuit.
 

Thevenin is commonly used for voltage analysis while Norton is used in current analysis.
You could use other circuit solving methods to identify Vth, Rth, and In.