f(x,y) = xe^[-x(y+1)] for x>0, y>o. = 0 otherwise. Show by calculation, the mean of Y does not exist. hello, I am just double checking a homework question. I am getting different answers with different integration rules. Not sure what to use. My own initial working out is using integral rule (integral of xe^ax dx = [(x/a) – (1/a^2)]e^ax . COuld someone please help out with a fresh and accurate look? I have had two tutors on here give me incorrect working out with minor mistakes and not explain what rules they are using.