Answer:
[tex]\huge\boxed{\sf -\frac{3}{5} }[/tex]
Step-by-step explanation:
[tex]\displaystyle \frac{21\sqrt{5} }{-7\sqrt{125} } \\\\125 \ can \ be \ written \ as \ 5 \times 5 \times 5\\\\= \frac{21\sqrt{5} }{-7\sqrt{ 5 \times 5 \times 5} } \\\\= -\frac{3\sqrt{5} }{\sqrt{5^2} \times \sqrt{5} } \\\\= -\frac{3\sqrt{5} }{5\sqrt{5} } \\\\= -\frac{3}{5} \\\\\rule[225]{225}{2}[/tex]
Hope this helped!
~AH1807
