[tex]U=ultima\,\,cifra \\ U( 3^{71}* 4^{62}) = \\ =U(3^{71})*U(4^{62})= \\ =U(3^{68+3})*U(4^{2*31})= \\ = U(3^{68}* 3^{3} )*U((4^{2})^{31})= \\ = U(3^{4*17}* 27 )*U((4^{2})^{31})= \\= U((3^{4})^{17}* 27 )*U((4^{2})^{31})= \\= U(81^{17})*U( 27)*U(16^{31})= \\ = U(1*7*6)=U(42)=2 [/tex]
