Find all numbers for which the rational expression is not defined

4x /(x^2-2x-15)        factor the denominator as  (x - 5)(x +3)

And since anything that makes the denominator 0, is undefined......then this rational function will be undefined when x = 5 or x = -3

See the graph, here: https://www.desmos.com/calculator/81t61hpgz7

Hello Guest!

Find all numbers for which the

rational expression is not defined.

4x / (x² - 2x - 15)

The rational expression is undefined

when the denominator is zero.

x² - 2x - 15 = 0

$x = {2 \pm \sqrt{4+60} \over 2}$

$x= \frac{2\pm 8}{2}$

$x_{1}= 5\ \ x_{2}= - 3$

The rational expression is undefined when

$x\in \left\{5, -3 \right\}$

Greeting asinus :- )  !