Answer:
[tex]\large \boxed{\text{7.428 in}}[/tex]
Step-by-step explanation:
[tex]\begin{array}{rcl}D & = & 0.145 r^{2}\\8 & = & 0.145 r^{2}\\55.17 & = & r^{2}\\r & = & \sqrt{55.17}\\& = & \textbf{7.428 in}\\\end{array}\\\text{The radius is $\large \boxed{\textbf{7.428 in}}$ when the depth is 8 in.}[/tex]
The graph shows the profile of your parabolic listening device,
