Let X1 and X2 have the joint pdf h(x1, x2)= 2e^(-X1-X2), 0<X1<X2<infinity, zero elsewhere. Find the joint pdf of Y1=2X1 and Y2=X2-X1.
I'm having trouble with transforming the boundaries.
This solution is provided in 71 words in an attached .doc file. It uses step-by-step equations to find the joint probability mass function.