Answer
$4.5$ miles long
Work Step by Step
The Pythagorean theorem is $a^2+b^2=c^2$ to solve for the hypotenuse of a right triangle. We are given that the rectangular park is 4 miles long and 2 miles wide, so we plug in those values to the formula.
$4^2+2^2=c^2$
$16+4=c^2$
$20=c^2$
$c=\sqrt {20}$
$c=2\sqrt 5$
$c\approx4.5$
