From the given functions, let's determine the function which is symmetric about the y-axis.
The line of symmetry can be said to be the axis which passes through the center of function that divides it into two equal halves.
We have the given graphs:
From the three graphs shown above, the graph which the y-axis divides into two equal halves is the graph of f(x) = x².
Therefore, the function which is symmetric about the y-axis is f(x) = x².
ANSWER:
f(x) = x²