Let a,b,c be three real numbers. Then the following system of equations in x y and z:
x2/a2 + y2/b2 - z2/c2 = 1
x2/a2 - y2/b2 + z2/c2 = 1
-x2/a2 + y2/b2 + z2/c2 = 1 has
i) no solution ii) unique solution
iii) infinitely many solution iv) none of these
