Question

Determina numarul natural n pentru care 1+2+3+...+n = 666

Answer 1

Răspuns:

1+2+3+..+n=666

[n•(n+1)]/2=666

n²+n/2=666

n²+n=666•2

n²+n=1332

n²+n-1332=0

∆=1-4•1•(-1332)=1+5328=5329

n1= -b-√∆/2a= -1-73/2= -74/2= -37

n2= -b+√∆/2a= -1+73/2 = 72/2= 36

==> n=36