Side remark: The completing the square trick can be easily generalised to completing the cube. A few additional straightforward manipulations (substitutions) re

Side remark: The completing the square trick can be easily generalised to completing the cube. A few additional straightforward manipulations (substitutions) result in something called a reduced cubic. You can then express the reduced cubic equation as cosh(3 acosh(x)) = C for some constant C (or you can use the function "cos" instead of "cosh") and solve for x.