[tex]f(x) = 5x-12[/tex]
[tex]f(-x) = 5(-x)-12 = -5x-12[/tex]
[tex]-f(x) = -(5x-12) = -5x+12[/tex]
[tex]-f(-x) = -(5(-x)-12) = -(-5x-12) = 5x+12[/tex]
This is probably asking you to consider the symmetry of f(x). If f(x) is equal to f(-x), then f is symmetric about the origin. If f(x) is equal to -f(x), then f is symmetric about the y-axis.
