diagonal of a rectangle

Since a diagonal that cuts a rectangle in 2 right triangles we can apply the Pythagorean Theorem.

$a^2 + b^2 = c^2$

From the question we know that $c =5\sqrt{10}$ then squaring it we get c=250.

$5^2$ =25 and 250-25=225

$\sqrt{225}$ = 15 and $15*5=75$