Figure that are congruent are shapes are the same size and shape. So when two formed congruent triangles are both together they fit just right.
An acute triangle.
A right angled triangle.
what is the congruent diagonals each of which divides the figure into two congruent isosceles right triangles
A square has 4 congruent sides and 4 right angles
It is a square
Not sure about angels, but if angles will satisfy you, the answer is a rectangle
A.K.A. a square
The right triangle.