Question

Find all the values of x that are not in the domain of f.

Answer 1

The values of x that are not in the domain of f are those that cannot be used because they leave an undefined output value, that means those that that leave the denominator of the function equal to zero.

`x^2-3x-40=0`

Factoring we have:

`(x+5)(x-8)=0`

This expression is zero if any of the factors is zero, then:

`x+5=0`
`x=-5`

Or

`x-8=0`
`x=8`

The values of x that are not in the domain of f are -5 and 8.