1)
ab +ba = x²
10a+b +10b+a = x²
11a+11b = x²
11(a+b) = x²
a+b = 11 ca sa fie patrat perfect
atunci a apartine multimii { 2,3,4,5,6,7,8,9}
si B apatine multimii {9,8,7,6,5,4,3,2}
2. 5625 = 3x3x5x5x5x5
1728 = 2x2x2x2x2x2x3x3x3
numarul se va termina in 4 zerouri deoarece avem de 4 ori 5x2 = 10
10x10x10x10=10000