Section 2.4
X-axis: replace y with –y. Simplify. If you get an equation = to what you started with, the function is symmetric to the x-axis. Y-axis: replace x with –x. Simplify. If you get an equation = to what you started with, the function is symmetric to the y-axis. Origin: replace x with –x AND y with –y. Simplify. If you get an equation = to what you started with, the function is symmetric to the origin.
Test for symmetry: y = |x| - 2 X-axis: -y = |x| - 2y = -|x| + 2 This is not the same, so the function is not symmetric to the x-axis. Y-axis: y = |-x| - 2y = |x| - 2 This is the same, so the function is symmetric to the y-axis. Origin: -y = |-x| - 2y = -|x| + 2 This is not the same, so the function is not symmetric to the origin.
Test for symmetry: 5x – 5y = 0 X-axis: no Y-axis: no Origin: yes
A function is EVEN if it is symmetric to the Y-axis. A function is ODD if it is symmetric to the Origin.
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