Răspuns :
U(5n) = 0 sau 5
=>U(5n+3) = 3 sau 8.
U(0²) = 0, U(1²) = 1, U(2²) = 4, U(3²) = 9, U(4²) = 6, U(5²) = 5, U(6²) = 6, U(7²) = 9, U(8²) = 4, U(9²) = 1
Ultimele cifre ale unui patrat perfect pot fi doar 0,1,4,5,6,9
=> √(5n+3) ∈ R \ Q, ∀ n ∈ N
U(5n) = 0 sau 5
=>U(5n+3) = 3 sau 8.
U(0²) = 0, U(1²) = 1, U(2²) = 4, U(3²) = 9, U(4²) = 6, U(5²) = 5, U(6²) = 6, U(7²) = 9, U(8²) = 4, U(9²) = 1
Ultimele cifre ale unui patrat perfect pot fi doar 0,1,4,5,6,9
=> √(5n+3) ∈ R \ Q, ∀ n ∈ N