Răspuns:
Explicație pas cu pas:
St 2+4+6+8+.....+3880-1-3-5-7-9-.....-1431 =
St = 2 ( 1+2+3+4+...1940) - ( 1+3+5+7+9+...1431)
S₁ = 1+2+3+4+...1940
S₁ = n*(n+1)/2
S₁ = 1940*1941/2
S₁ =1.882.770
S₂ = 1+3+5+7+9+...1431
S₂ = n*n unde 2n-1 = 1431 si n=716
S₂ = 716*716
S₂ =512.656
St = 2*S₁ - S₂
St = 2 * 1.882.770 - 512.656
St =3.252.884
Succes !!