Question

a,tính

A=\(\sqrt{\left(1-2\sqrt{5}\right)^2}\)-\(\sqrt{20}\)

Answer 1

\(A=\sqrt{\left(1-2\sqrt{5}\right)^2}-\sqrt{20}\)

\(=\left|1-2\sqrt{5}\right|-2\sqrt{5}\)

\(=2\sqrt{5}-1-2\sqrt{5}\)

\(=-1\)

Answer 2

\(A=\sqrt{\left(1-2\sqrt{5}\right)^2}-\sqrt{20}\\ =\left|1-2\sqrt{5}\right|-2\sqrt{5}\left(1\right)\)

\(Vì : 1<2\sqrt 5=>1-2\sqrt 5<0=>|1-2\sqrt5|=-(1-2\sqrt5)=2\sqrt5 -1\)

\(\left(1\right)=>2\sqrt{5}-1-2\sqrt{5}=-1\)

\(Vậy A=-1\)

Answer 3

\(=2\sqrt{5}-1-2\sqrt{5}=-1\)