# Unit Circle: y-axis Symmetry

Author:
Whit Ford
Symmetry in Trigonometry The green slider determines the angle , with a range of to . After using the green slider to vary the angle a bit, what function of do you think describes the angle in the graph below? moves in the opposite direction from , starting from and moving back towards .
The angle is equal to . Move the green slider to the left and right, and watch how points and are always symmetrical to one another about the y-axis. If two points, such as and , are symmetric about the y-axis, - How must their x-coordinates be related? - How must their y-coordinates be related? The graph above illustrates the y-axis symmetry displayed by the angles and Pairs of points that are symmetric about the y-axis will always: - have x-coordinates that are the negative of one another - have the same y-coordinates Note that negative angles are displayed as their positive equivalents. If you wish to use other applets similar to this, you may find an index of all my applets here: https://mathmaine.com/2010/04/27/geogebra/