Question

(\(2\sqrt{5}\)-\(\sqrt{7}\))²

Answer 1

\(\left(2\sqrt{5}-\sqrt{7}\right)^2=20-4\sqrt{35}+7=27-4\sqrt{35}\)

Answer 2

Ta có:

 \(\left(2\sqrt{5}-\sqrt{7}\right)^2\)

\(=\left(2\sqrt{5}\right)^2-2.2\sqrt{5}.\sqrt{7}+\left(\sqrt{7}\right)^2\)

\(=4.5-4\sqrt{5.7}+7\)

\(=20-4\sqrt{35}+7\)

\(=27-4\sqrt{35}\)