Aratati ca nr N= 2001+2 (1+2+3+...+2000) este patrat perfect

Răspuns :

N= 2001+2 (1+2+3+...+2000)
N = 2001 + 2× 2000×2001:2
N = 2001 + 2000×2001
N = 2001 ×(1 + 2000)
N = 2001 × 2001
N = 2001^2 p.p