[tex] \frac{ x^{2} +(x+1) ^{2} }{2}=12,5=> x^{2} + (x+1)^{2} =25<=> \\ \\ <=> x^{2} + x^{2} +2x+1=25<=> 2x^{2} +2x=24=> x^{2} +x=12<=> \\ \\ <=>x(x+1)=12.[/tex]
Tinand cont de faptul ca x∈N si x(x+1)=12 => x=3.
Deci numerele cautate sunt 3²=9 si 4²=16.
