$|BD|=a$, $|DC|=b$, $|ED|=h$ ve $|AD|=j$ olsun.
$\triangle{EBD}$'de Pisagor: $a^2+h^2=x^2$
$\triangle{ABD}$'de Pisagor: $a^2+j^2=10^2$
$j^2-h^2=10^2-x^2$ $(1)$
$\triangle{EDC}$'de Pisagor: $b^2+h^2=8^2$
$\triangle{ADC}$'de Pisagor: $b^2+j^2=12^2$
$j^2-h^2=12^2-8^2$ $(2)$
$(1)$ ve $(2)$'den, $10^2-x^2=12^2-8^2$
$x=2 \sqrt{5}$