9. Incorrect. The answer is true not false. To prove this proposition, it is necessary to calculte the marginal densities for x and y respectively and show that: f(x,y) = fX(x).fY(y), where fi(i) is marginal density function:fi(i) = ∫ba f(i,j)dj.
Therefore, (x,y) is a random vector with independent variables.