Let's name these angles.
∠ A = 72°
∠ B = 54°
∠ C = 54°
Now, in this triangle, two angles, i.e., ∠ B and ∠ C are same.
According to the properties of triangle, sides opposite to two equal angles in a triangle are also equal, which means the two sides opposite to 54° in the figure will be equal.
=> AB = AC
Now, if there are two equal sides in a triangle then the triangle is called Isosceles Triangle.
So, the above triangle is an Isosceles Triangle.
