The most difficult mathematics is that which you do not know. A surprising amount of mathematics is actually easy once you've learned it. Of course, once you learn the easy stuff, then you have to start tacking the deep stuff, and that gets harder.
An isosceles triangle has two sides of equal length. An isosceles triangle also has two angles of the same measure; namely, the angles opposite to the two sides of the same length; this fact is the content of the isosceles triangle theorem, which was known by Euclid.
Use isosceles and equilateral triangles. Using the Base Angles Theorem. A triangle is isosceles when it has at least two congruent. sides. When an isosceles triangle has exactly two congruent. sides, these two sides are the legs. The angle formed by the. legs is the vertex angle. The third side is the base of the. isosceles triangle.