2. Fie functia f:R ⇒R , f(x)=x³ +2x. Aratati ca f(-x)= -f(x) , oricare x apartine R
4. Fie functia f:R ⇒R , f(x)=x³ +2x. Calculati f(-20)+f(-10)+f(0)+f(10)+f(20)
5.Fie functia f:R*⇒R , f(x)= \frac{x^{2}+1}{x} .Aratati ca f(x)=f(\frac{1}{x} ), oricare x apartine R*