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) = f_X(x).f_Y(y), where f_i(i) is marginal density function:f_i(i) = ∫^b_a f(i,j)dj.

Then:

Therefore, (x,y) is a random vector with independent variables.