Extraneous solutions are roots of the polynomial which when substituted to the expression, the expression is invalid or not true. One example is x - 6 =

. We square both sides, x^2 - 12x + 36 = x.
x^2 - 13x + 36 = 0. This is equal to (x-4)*(x-9) = 0. The roots are 9 and 4. The extraneous solution is 4 since when we substitute 4 to the original expression, there is no equality.