Drawing the altitude of an equilateral triangle decomposes the equilateral triangle into two congruent triangles

They are right triangles with acute angles of 30 and 60 degrees

These congruent angles make all triangles with angles 30, 60, and 90 degrees similar by the Angle-Angle Triangle Similarity Theorem

In 30-60-90, shortest side = 1 unit, hypotenuse 2 units since the triangle can be thought as half of an equilateral triangle