In Exercise 5.9 , we determined that
$$f\left(y_{1}, y_{2}\right)=\left\{\begin{array}{ll}6\left(1-y_{2}\right), & 0 \leq y_{1} \leq y_{2} \leq 1 \\0, & \text { elsewhere }\end{array}\right.$$
is a valid joint probability density function. Are $Y_{1}$ and $Y_{2}$ independent?