The formula of an area of a square:
[tex]A=a^2[/tex]
a - a side
We have [tex]A=450\ in^2[/tex]
substitute:
[tex]a^2=450\to a=\sqrt{450}\\\\a=\sqrt{225\cdot2}\\\\a=\sqrt{225}\cdot\sqrt2\\\\\boxed{a=15\sqrt2\ in}[/tex]
Used:
[tex]\sqrt{a\cdot b}=\sqrt{a}\cdot\sqrt{b}[/tex]