Question

determina numerele naturale de forma xy stiind ca xy+yx=77

Answer 1

⇒x+y=7
⇔xy∈{16,25,34,43,52,61}
pentru solutia 0+7 nu convine ,deoarece x cifra⇒x nenul

Answer 2

$\overline{xy}+\overline{yx}=77 \\\\ 10x+y+10y+x=77 \\\\ 11x+11y=77 \ \ |:11 \\\\ x+y=7 \\ x,y \in N \\\\ \Longrightarrow S_{(x;y)}=\{ (1;6);(2;5);(3;4);(4;3);(5;2);(6;1) \}$