Question

Subiectul 2, ex 4, b va rog frumos

Answer 1

f:R->R; f(x)=2x+1

N=f(0)+f(1)+f(2)+....+f(10)

N=2·0+1 +2•1+1 +2•2+1 +2•3+1 +....+2•10+1

N=2(1+2+3+....+10)+11; (de la 0 la 10 sunt 11 numere, deci avem 11 de 1)

N=2·10•11/2 +11

N=121

N=11²; patrat perfect