Vom determina ultima cifră a fiecărui termen.
[tex] \it u(9^{1996}) = u(9^2)^{998} =u(81)^{998} = u(1^{998}) =1
\\ \\
u(7^{1992}) u(7^4)^{498} = u(2401)^{498} = u(1^{498}) = 1
\\ \\
u(9^{1996} -7^{1992} ) = 1-1 = 0 \Rightarrow (9^{1996} -7^{1992}) \ \vdots\ 10 [/tex]