Chapter 11 - Section 11.2 - Solving Quadratic Equations by Completing the Square - Exercise Set - Page 777: 55

15.62 ft by 25.62 ft

$x*(x+10)=400$ $x^2+10x-400=0$ $x=(-b±\sqrt {b^2-4ac})/2a$ $x=(-10±\sqrt {10^2-4*1*-400})/2*1$ $x=(-10±\sqrt {100+1600})/2$ $x=(-10±\sqrt {1700})/2$ $x=(-10±\sqrt {4*425})/2$ $x=(-10±2\sqrt {425})/2$ $x=(-5±\sqrt {425})$ We want to find a distance, so we want only positive distances. $x=-5+\sqrt {425}$ $x=-5+20.615$ $x=15.615$