A right-angled isosceles triangle ABC is given. Determine what kind of figure will turn

A right-angled isosceles triangle ABC is given. Determine what kind of figure will turn out when this triangle is symmetrical about the straight line containing its leg.

You will also get an isosceles right-angled triangle with an area equal to twice the area of the original triangle.
Let’s call the vertices of the original triangle ABC so that the angle B is right.
The angles at the base of A and C for this triangle are the same and equal to 45 degrees (180-90) / 2.
Then, with symmetry about the leg AB, the angle A of the new triangle will turn out to be 45 * 2 = 90 degrees, that is, it will be right.