Answer
$-\dfrac{\sqrt { 15}}{5}$
Work Step by Step
Rationalize the denominator by multiplying $\sqrt5$ to both the numerator and the denominator:
$\dfrac{-\sqrt 3}{\sqrt 5}=\dfrac{-\sqrt 3}{\sqrt 5} \cdot \dfrac{\sqrt 5}{\sqrt5}$
Simplify.
$=\dfrac{-\sqrt 3\cdot \sqrt 5}{(\sqrt 5)^2}$
Use the rule $\sqrt{a} \cdot \sqrt{b}=\sqrt{a\cdot b}$:
$=\dfrac{-\sqrt {3\cdot 5}}{5}$
$=-\dfrac{\sqrt { 15}}{5}$
Hence, the correct answer is $-\frac{\sqrt { 15}}{5}$.
