IKMC 2019 - Grades 11-12 - Self-study Question 27

Question 27

Inside square ABCD is a path DEFB with $DE\perp EF$, $EF\perp FB$ as shown. Given $DE=5$, $EF=1$, $FB=2$, what is the square’s side length?

Question illustration

$3\sqrt2$
$\frac{7\sqrt2}2$
$\frac{11}2$
$5\sqrt2$
Another value