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7: Trigonometry

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    Learning Objectives

    • Sketch angles in standard position measured in either degrees or radians.
    • Identify coterminal angles and produce a sketch.
    • Identify reference angles and produce a sketch.
    • Use the equation of a circle to compute points on the circle as ordered pairs.
    • Understand how special right triangles, together with symmetry, yields the ordered pairs on the unit circle.

    • 7.1: The Unit Circle
      The core concepts of trigonometry are developed from a circle with radius equal to 1 unit, drawn in the xy-coordinate plane, centered at the origin. This circle is given a name: the unit circle. An angle is in standard position if its initial side is along the positive x-axis and its vertex is at the origin: point (0,0). An angle that rotates in the counter-clockwise direction is a positive angle. An angle that rotates in the clockwise direction is a negative angle.
    • 7.2: Reference Angles
      A reference angle is the positive acute angle between the terminal side of the standard angle and the x-axis. The word reference is used because all angles can refer to QI. That is, memorization of ordered pairs is confined to QI of the unit circle. If a standard angle has a reference angle of 30˚, 45˚, or 60˚, the unit circle's ordered pair is duplicated, but the sign value of x or y may need adjustment, depending on the quadrant of the terminal side of the standard angle.
    • 7.3: Radians
      Angles can be measured in units of degrees or radians. Once you get the hang of radians, your trigonometric calculations are quick and easy. Using radians for angles, rather than degrees, is the key to gain fluidity in trigonometry. They are simpler to use than degrees. Notice the shared denominators from one quadrant to the next. Also notice the denominator of an angle matches its own reference angle’s denominator.

    This page titled 7: Trigonometry is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Jennifer Freidenreich.

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