=+f ( - ;

a, u) + f( ; a,c) = f( ;

a, u +v).

Note that (20.46) is f(x; 4, n/2), and from (20.48) deduce again that (20.46) is the density of x2. Note that the exponential density (20.10) is f(x; «, 1), and from (20.48) deduce (20.39) once again.