x squared - i = 0

$\displaystyle x^2-i=0$

$\displaystyle x^2=i$

$\displaystyle x=\sqrt{i}$

$\displaystyle x=\sqrt{\sqrt-1}$

$\displaystyle x=\pm(\frac{1+i}{\sqrt2})$

What symbol(s) is(are) needed to make Delimiters (. . .) bigger to completely encompass fraction?