Răspuns:
Explicație:
S=1+3+5+...+x
S=x+...+5+3+1
----------------------
2S=(x+1)+(x+1)+...+(x+1)
aflam cati termeni sunt:
(x-1):2+1
=> 2S=(x+1)[(x-1):2+1]
=> 169*2=(x+1)(x-1):2+(x+1) /*2
=> 169*4=x²-1+2x+2
=> 676=x²+2x+1
=> (x+1)²=676
=> x+1=±√676
=>x+1=±26 => x=±26-1
=> x1=-26-1=-27
=> x2=26-1=25
Se vede clar ca numerele respect un sir pozitiv => x=25
Verificare:
nr termeni: (25-1):2+1=24:2+1=12+1=13
2S=(25+1)*13
S=26*13:2
S=13*13
S=169
Succes la scoala
