QUASI doubt !!!

[Anjali]

The function y = x^2, x>0, is:
 (a) Quasi-concave and quasi-convex   (b) Quasi-concave but not quasi-convex (c) Quasi- convex but not quasi-concave (d) Neither quasi-concave nor quasi-convex

The answer is A.
While solving for bordered hessian matrix , Iam getting D1= -4x^2 , and D2=0
Now how do we arrive at the conclusion that it's both quasi concave and quasi convex ?

[kangkan]

refer to chiang page 364.(part of quasi convexivty)