Triangles
The Right Triangle: the most basic and important type of triangle that you will encounter in Astronomy (and in Physics) is the right triangle. The right triangle is a triangle that has one 90 degrees angle. Since the sum of the angles in a triangle must be 180 degrees, this tells that the other two angles in a right triangle must add up to 90 degrees. Many special trigonomec relationships between the sides and the angles emerge as a result of this special 90 degrees angle. One of these relations is the so called Pythagorean Theorem. the relation is: a2 + b2 = c2
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Triangles can be classified either according to their sides or according to their angles. All of each may be of different or the same sizes any two sides or angles may be of the same size there may be one distinctive angle.