Question

Chứng minh √20=2√5

Answer 1

Ta có 

\(2\sqrt{5}=\sqrt{4}.\sqrt{5}=\sqrt{4.5}=\sqrt{20}\)

 

Answer 2

\(Gi\text{ả}s\text{ử}\sqrt{20}=2\sqrt{5}\Rightarrow20=\left(2\sqrt{5}\right)^2\Rightarrow20=2^2.\left(\sqrt{5}\right)^2\Rightarrow20=4.5\Rightarrow20=20\)

Vậy căn 20 = 2 nhân căn 5