If a graph of a function has a line of symmetry, the function be even about line. This means that if the function is transformed so that the line becomes the y axis, we will be able to write
where
for some number
Suppose
shown below.
The graph has a vertical line of symmetry with equation
Suppose we write
then
so that the line
is the line
Write
thenand
is even so
oris a line of symmetry.