Given, cos2A+cos2C=sin2B Obviously it is not an equilateral triangle because A=B=C=60° does not satisfy the given condition. But B=90°, then sin2B=1 and cos2A+cos2C=cos2A+cos2(
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2
−A) =cos2A+sin2A=1 Hence, this satisfies the condition, so it is a right angled triangle but not necessarily isosceles triangle.