Answer:
x=9
x=-9
Step-by-step explanation:
The x intercept or roots are x values that makes the f(x) equal 0. So in order words, to find the x intercept. Set the equation equal 0.
[tex] {x}^{2} - 81 = 0[/tex]
We can approach this problem 2 ways
Way 1: Differnece of Squares
Recall that
[tex]a {}^{2} - {b}^{2} = (a + b)(a - b)[/tex]
Since x^2 and 81 are both perfect squares and 81 is negative, we can say that
[tex](x + 9)(x - 9) = 0[/tex]
Set each equation to zero
[tex]x = 9[/tex]
[tex]x = - 9[/tex]
Way 2: Take square root of both sides
[tex] {x}^{2} - 81 = 0[/tex]
[tex] {x}^{2} = 81[/tex]
Next step, take square root of both sides. Square root produce negative and positive solutions so
[tex]x = 9[/tex]
or
[tex]x = - 9[/tex]
