The joint pdf of random variable x and y is given by fxx(x,

The joint pdf of random variable x and y is given by f_xx(x, y) = ke^{– (ax + by)} u(x).u(y)

F_xy(x, y) =		^∞		^∞	f_xy(x, y)dx dy
		-∞		-∞

1 =		^∞		^∞	ke^{–(ax + by)} u(x).u(y)dy.dx
		-∞		-∞

1 =		^∞		^∞	ke^–ax.e^–by.dydx
		₀		₀

1 =	k
	ab

or k = ab