What do these two shapes have in common?
Let’s call them triangle one and triangle two. On triangle one I noticed these two lines. These dashes on the triangle tell us that these two lines of this triangle are the same length. They are congruent.
And when a triangle has two congruent sides, we call it an isosceles triangle. Triangle two also has two sides labelled as congruent. This makes triangle two an isosceles triangle. Maybe you’re thinking, “Wait! These sides are not the same length.”
And that would be true. The two triangles are not congruent. They’re not the same size and the same shape.
But because each of the triangles has two set of congruent sides, they are both isosceles triangles.