If cos2A+cos2C=sin2B, then â–³ ABC is
[MP PET 1991]
Right angled
Trick: Obviously it is not an equilateral triangle because A=B=C=60o does not satisfy the given condition. But B = 90o then sin2 B = 1 and
cos2A+cos2C=cos2A+cos2(π2−A)
=cos2A+sin2A=1
Hence this satisfy the condition, so it is a right angle triangle but not necessarily isosceles.