Two components of minicomputer have the following joint pdf for their useful lifetime X and Y: f(x, y)=\left\{\begin{array}{ll} \frac{1}{4} e^{-(x+y) / 2} & x>0, y>0 \\ 0 & \text {

elsewhere } \end{array}\right. Find the covariance of X and Y. Round your final answer to two decimal places. (Hint: do you notice something special about the form of the joint pdf?)