Question

Find the difference sqrt 20- sqrt 80

Answer 1

First you need to reduce each square root.  In each case, find the largest perfect square factor under the radical.  

in the case of sqrt(20), that boils down to 4*5, so sqrt(20)=sqrt(4)*sqrt(5), or 2sqrt(5).

sqrt(80) = sqrt(16)*sqrt(5) = 4sqrt(5).

Final answer:  subtract 4 sqrt(5) from 2 sqrt(5).  Can you do this?

Answer 2

It is letter B. aka -2√5