ANSWER
[tex]\frac{ - 12x \sqrt{x} - 120x}{ x - 100} [/tex]
EXPLANATION
The given function is
[tex] \frac{ - 12x}{ \sqrt{x} - 10 } [/tex]
In the denominator we have
[tex] \sqrt{x} - 10[/tex]
The conjugate of this surd is
[tex] \sqrt{x} + 10[/tex]
To rationalize this function, we multiply both the numerator and the denominator by the conjugate surd.
[tex]\frac{ - 12x (\sqrt{x} + 10)}{ (\sqrt{x} - 10)(\sqrt{x} + 1)} [/tex]
We apply the identity
[tex] (a + b)(a - b) = {a}^{2} - {b}^{2}[/tex]
in the denominator.
This implies that,
[tex]\frac{ - 12x (\sqrt{x} + 10)}{ (\sqrt{x})^{2} - {10}^{2} } [/tex]
[tex]\frac{ - 12x \sqrt{x} - 120x}{ x - 100} [/tex]