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 ISOSCELES RIGHT TRIANGLE . A N ISOSCELES RIGHT TRIANGLE is one of two special triangles. (The other is the 30Â°-60Â°-90Â° triangle.) The student should know the ratios of the sides. (An isosceles triangle has two equal sides. See Definition 8 in Some Theorems of Plane Geometry. The theorems cited below will be found there.) Theorem. In an isosceles right triangle the sides are in the ratio 1:1:. Proof. In an isosceles right triangle, the equal sides make the right angle. They have the ratio of equality, 1 : 1. To find the ratio number of the hypotenuse h, we have, according to the Pythagorean theorem, h2 = 12 + 12 = 2.