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.
The altitude drawn on the base of an isosceles triangle helps in finding the area of the triangle, which is half the product of the altitude and the base. If all three sides and angles of a triangle are equal, it is called an equilateral triangle. Thus, an equilateral triangle is also an isosceles triangle.