A line of symmetry is a line that divides a figure into two parts such that each part is the mirror image of the other. In other words, if we flip one side of the figure over the line of symmetry, it should match up exactly with the other side.
Let's look at a 2 examples.
In the first image provided, notice that if we flip the left side of the figure over the right side, the two sides will not match up so this is not a line of symmetry.
In the second image, if we flip the left side of the line on to the right side, it matches up exactly so it's a line of symmetry.
