Determine the covariance and correlation for the joint probability density function f_(xY)(x,y)=e(-x-y) over the range 0.0 and 0.
a) Covariance: 1, Correlation: 0
b) Covariance: -1, Correlation: 0
c) Covariance: 0, Correlation: 1
d) Covariance: 0, Correlation: -1