a) thay x=\(\frac{-1}{3}\) vào biểu thức A ta có:

A=\(5.\left(\frac{-1}{3}\right)^3-3.\left(\frac{-1}{3}\right)^2-\frac{1}{3}\)

=\(5.\frac{-1}{27}-3.\frac{1}{9}+\frac{1}{3}\)

=\(\frac{-5}{27}-\frac{3}{9}+\frac{1}{3}\) 

=\(\frac{-14}{27}+\frac{1}{3}\)

=\(\frac{-5}{27}\)

mik