(1) is insufficient b/c do not know anything about X,Y
(2) is insufficient for the same reason above
(1)+(2), (Z^2)>1/(XY) from (1) we know that Z=1/(XY)
so (Z^2)>Z, solve the inequality, get (Z-1)Z>0, get critical point Z=1,0, then try Z<0, Z between 0 and 1 and Z>1, we can see the inequality is right when Z<0 and Z>1