Let X1 and X2 be two continuous random variables with joint PDF fX1,X2. Let Y1 = X1 + X2 and Y2 = X1 - X2.
(a) Find the joint PDF of Y1 and Y2 in terms of fX1,X2.
Suppose, in addition, that X1 and X2 are independent standard normals.
(b) Show that Y1 and Y2 are independent and find their PDFs fY1 and fY2.