Chapter 10 - Radical Expressions and Equations - 10-4 Solving Radical Equations - Practice and Problem-Solving Exercises - Page 638: 53

Answer D

$\sqrt c^2-17=8$ Square both sides $c^2-17=64$ $c^2=81$ $c= \pm 9$ With $c=9$ $\sqrt 9^2-17=8$ $8=8$ With $c=-9$ $\sqrt (-9)^2-17=8$ $8=8$ Hence, the solutions of the equation are $x=\pm 9$. The correct answer is D.