Expansion of $\sqrt{(a+3i)^2+x^2}$ with $x,a\in \mathbb R,\ x>>a, 3$

Question

I know that if we only have $\sqrt{a^2+x^2}$ with $a,x\in \mathbb R,\ x>>a$, then we do the normal Taylor expansion around $\frac{a}{x}<<1$, but what if I want to expand something like $\sqrt{(a+3i)^2+x^2}$ with $x,a\in \mathbb R,\ x>>a, 3$? I do not know how to expand this. Thank you.