Question

TINH

\(\left(2\sqrt{5}+2\right)\left(2\sqrt{5}-\sqrt{2}\right)\)

Answer 1

\(\left(2\sqrt{5}+2\right)\left(2\sqrt{5}-2\right)=\left(2\sqrt{5}\right)^2-2^2=20-4=16\)

Answer 2

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

\(=20-2\sqrt{10}+4\sqrt{5}-2\sqrt{2}\)

Answer 3

      \(\left(2\sqrt{5}+2\right)\left(2\sqrt{5}-\sqrt{2}\right)\)     

\(=\left(2.1\sqrt{5.1}+2\right)\left(2.1\sqrt{5.1}-\sqrt{2.1}\right)\)

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

\(=20-2\sqrt{10}+4\sqrt{5}-2\sqrt{2}\)     

Phải không Phan Thị Hồng Nhung ?