the x value or x-values that we would plug in to get 0 so in this case we want the x values that makes f of x equal to 0 so all we need to do is set x squared minus 81 equal to 0 well this is a difference of perfect squares so we can factor it as x minus 9 times x plus 9 equals 0 which gives us the roots x equals 9 and x equals negative 9 these two roots give you f of x equals 0 so those two would be f of 9 equals f of negative 9 equals 0 so those are the 