zecile a , b sunt 1.2.3 ... sau 9
10a +b +10b +a -4a -4b = 7a + 7b = 7 ( a +b ) este patrat perfect daca = 7·7
⇒ a +b =7
a 1 2 3 4 5 6
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b 6 5 4 3 2 1
ab = 16 , 25,34 ,43, 52 ,61--------------------------------------------succes!--------------------------------------------