Question

For the given figure, which one is the mirror line, ${{I}_{1}}$ or ${{I}_{2}}$ ?

Answer 1

Hint: In order to solve this problem, we take the portion of the body on one side of a line and mirror it about the line. If we get the original figure by doing so, then that line is a mirror line. At first, we do it with the line ${{I}_{2}}$ and then with ${{I}_{1}}$.

Complete step by step solution:
Before starting with the solution, let us discuss the elements of symmetry and when a body is said to be symmetric or asymmetric. First, we will discuss the two major elements of symmetry, which are the line of symmetry and the axis of symmetry.
The line of symmetry is the imaginary line through the body which divides the body into two equal halves such that the parts on each side of the body are the mirror images of one another. While the axis of symmetry is an axis passing through the body about which the rotation of the body gives the exact identical figure as the initial one.
Now, starting with the given figure, if the portion of the body on one side of ${{I}_{1}}$ is taken, and mirrored about the line ${{I}_{1}}$ , we get,

Which is not the original figure. Now, if the portion of the body on one side of ${{I}_{2}}$ is taken, and mirrored about the line ${{I}_{2}}$ , we get,

Which is the original figure.
Thus, we can conclude that ${{I}_{2}}$ is the mirror line.

Note: The mirror line problems should be dealt with carefully. Sometimes, one line may seem like the mirror line, but it is not. Also, we can do another thing. If we fold the figure along the line and get a mirror image of the part folded, then that line is a mirror line.