Angle instandard position and reference angles: The reference angle is the acute angle formed by the terminal side of the given angle and the x-axis. Reference angles may appear in all four quadrants. The refernce angle is measured from the terminal side of original angle TO the x-axis, not the y-axis. Angles in quadrant I are their own reference angles. Now, move the slider and see the location of reference angle.

Now, Answer the following questions: How do you calculate reference angle algebraically? Answer: Angle in quadrant I, reference angle is angle itself. Angle in quadrant II, reference angle is [math] 180 degree - \theta[/math] Angle in quadrant III, reference angle is [math] \theta - 180 degree [/math] Angle in quadrant IV, reference angle is [math] 360 degree - \theta[/math] Vera Hu-Hyneman, SCCC selden, NY

In trigonometry the definition of an angle is changed from that used in elementary geometry. An angle can represent an amount of rotation and take any value. Positive angles are measued counterclockwise from the positive x-axis. Negative angles are measured clockwise from the positive x-axis.

Move the slider back and forth.