Question

detrerminati numarul natural n din egelitatea 1+5+9+...+n=231

Answer 1

Numarul de termeni: (n-1)/4 +1= n+3/4
Suma: (n+1)(n+3)/8=231
n^2+4n+3=1848
Delta: 16-4*3=16-12=4
1. (-4+2)/2=-1
2. (-4-2)/2=-3
Deci n={-3; 1}