Page "Equation" Paragraph 40

# Some functions can be applied to both sides.

Caution must be exercised to ensure that the operation does not cause missing or extraneous solutions.

For example, the equation has 2 sets of solutions: ( with any x ) and ( with any y ).

Raising both sides to the exponent of 2 ( which means, applying the function to both sides of the equation ) changes our equation into, which not only has all the previous solutions but also introduces a new set of extraneous solutions, with and x being any number.