Answer:
A. [tex]9\sqrt{10}[/tex]
Step-by-step explanation:
The given expression is [tex]-6\sqrt{10}+5\sqrt{90}[/tex]
Remove the perfect square from the second radical.
[tex]=-6\sqrt{10}+5\sqrt{9\times10}[/tex]
[tex]=-6\sqrt{10}+5\sqrt{9} \times \sqrt{10}[/tex]
This implies
[tex]=-6\sqrt{10}+15\sqrt{10}[/tex]
[tex]=(-6+15)\sqrt{10}[/tex]
[tex]=9\sqrt{10}[/tex]
The correct choice is A
