Consider matrix \({\rm{A}} = \left[ {\begin{array}{*{20}{c}} {\rm{k}}&{2{\rm{k}}}\\ {{{\rm{k}}^2} - {\rm{k}}}&{{{\rm{k}}^2}} \end{array}} \right]\) and vector \({\rm{x}} = \left[ {\begin{array}{*{20}{c}} {{{\rm{x}}_1}}\\ {{{\rm{x}}_2}} \end{array}} \right]\). The number of distinct real values of k for which the equation Ax = 0 has infinitely many solution is________