a)
[tex]e(x) = (x+3)²-(2x+1) \times (x-7)-(x+4) \times (4-x) = \\ x ^{2} + 6x + 9 - (2x ^{2} - 14x + x - 7) - (4x - x^{2} + 16 - 4x) = \\ x ^{2} + 6x + 9 - 2x ^{2} + 14x - x + 7 - 4x + x ^{2} - 16 + 4x = \\ 19x[/tex]
b)E(x)=19x=>E(n)=19n
[tex]e(n) \leqslant n ^{3} \\ 19n \leqslant n ^{3} \\ 19 \leqslant n ^{2} [/tex]
toate numerele de la 5 in sus
cumva,intervalul [5,+infinit)
