13. Correct. The answer is true. To obtain this model it is necessary to find the conditional density function, which is defined as follows:
First of all, we have to obtain the marginal density f1. It is obtained by fixing y and integrating with respect to x from x = y to x = 1. The result is, for 0 < y < 1:
for all other values of y, f1(x) = 0.
The conditional density function of x is, for 0 < y < 1: