Hey, We can see here 2 of the angles are equal and the third one is a right angle right? That means it is an isosceles triangle since they have 2 equel angles and a right anlgle.
Another feature of the isosceles triangle is that 2 sides are equal. We are given one side is 5.5 right? So the side BC has to be 5.5 or the side AB has to be 5.5 In isosceles triangles the side opposite to the 90 degree angle is the hypotenuse.This means it is the longest angle. So it has to be AB which is equal to 5.5 since BC is the hypotenuse.
