<PRE><B>Question 1016797</B>
You messed-up about half-way down your steps.  After squaring the first time, simplify, as you did, but then you need to isolate the radical still present and square both sides again.


Start from here:
{{{-x-80=-18*sqrt(2x+5))}}}


Instead of trying to completely isolate the radical, just isolate the entire radical term, .... AND SQUARE BOTH SIDES THAT WAY.

{{{x+80=18*sqrt(2x+5)}}}----square both sides!
Simplify, and solve.</PRE>