Question

E(x)=5supra xpatrat+4-4supra luix patrat+5

Answer 1

Aducem la o forma mai simpla:
$E(x)=\frac{5}{x^2+4}-\frac{4}{x^2+5}=\frac{5(x^2+5)-4(x^2+4)}{(x^2+4)(x^2+5)}=\frac{x^2+9}{(x^2+4)(x^2+5)}=\frac{x^2+9}{x^4+9x^2+20}$