The rules of a special right triangle concern the angles of the triangle. A special right triangle is one with the angles 30, 60 and 90 degrees. A right triangle with the angles 45, 45 and 90 degrees is another special triangle.
The special right triangle finds application in trigonometry. It becomes easier to calculate the values of trigonometric functions when a right triangle has these angles. The six trigonometric functions are sine, cosine, tangent, cosecant, secant and cotangent.
The values of trigonometric functions depend on the values of the angles other than the right angle. The ratios of the lengths of the sides of the right triangle give these six trigonometric functions.