The error happens at step 4
Instead of [tex]x = \sqrt{36}[/tex], it should be [tex]x = \pm\sqrt{36}[/tex] which leads to [tex]x = \pm 6[/tex]
The two solutions are x = 6 or x = -6.
Notice that x^2 = 6^2 = 36 and x^2 = (-6)^2 = (-6)*(-6) = 36. The two negatives cancel out.
