TRIGONOMETRY BASICS

The Circle

A circle is something everyone seems to understand because we see it in everywhere. Simply look at the full moon, a wheel, or the iris of an eye and you can see the circle in its natural glory.

The circle has several properties that make it the starting point of our journey. First of all, it has a constant relationship (or ratio) of the radius of the circle to the circumference that is embodied in the constant PI (pronounced “pie”), which equals around 3.14159. The formula for the circumference, or distance around the circle, is 2*PI*R, where R is the radius of the circle. The radius is simply the length of a straight line drawn from the center of the circle to the outer edge (see diagram 1). But 2R equals the diameter of the circle (D), which is a line that cuts the circle into 2 equal pieces, so the circumference also equals PI * D (see diagram 2).

Diagram 1: The Circle Radius

Diagram 2: The Circle Diameter

The Triangle

The most basic planar shape, a triangle has the fewest sides (3) needed to enclose a plane. The primary triangle types are:

  • Equilateral (has all equal angles, at sixty degrees each)

  • Isosceles (has two sides equal length)

  • Right (has one ninety degree angle)

  • Scalene (no side equal)


 

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