An isosceles triangle is a triangle
that has 2 sides and 2 angles the same
length. Two of the angles are the same measure also. The triangle to the right is isosceles.
For example, if you have a triangle that is isosceles and has one angle
that is 100 degrees, what are the other 2 angles? Well, the other 2 angles sum to 80 degrees (180 - 100), and both of the other 2 angles are the same, so the sum of the other 2 identical angles is 80 degrees, so each of the other angles must be 40 degrees!
To learn more about triangles, see the triangle notes.