OBVIOUS. TRICK: Obviously it is not an EQUILATERAL triangle because A=B=C=60o does not SATISFY the given condition. But B = 90o then \[{{\sin }^{2}}B=1\] and \[{{\cos }^{2}}A+{{\cos }^{2}}C={{\cos }^{2}}A+{{\cos }^{2}}\left( \frac{\pi }{2}-A \right)\,\] \[=\,{{\cos }^{2}}A+{{\sin }^{2}}A=1\] Hence this satisfy the condition, so it is a right ANGLE triangle but not necessarily isosceles.