Peter Linz Edition 4 Exercise 4.1 Question 6 (Page No. 109)

Question

The symmetric difference of two sets $S_1$ and $S_2$ is defined as $S_1 θ S_2 =$ {$x: x ∈ S_1$ or $x ∈ S_2,$ but $x$ is not in both $S_1$ and $S_2$}.
Show that the family of regular languages is closed under symmetric difference.