Question

Tính: \(\sqrt{3-\sqrt{5}}.\sqrt{3+\sqrt{5}}\)

Answer 1

bạn dùng hằng đẳng thức (a+b)(a-b)=a^2+b^2 thôi

Answer 2

\(\sqrt{3-\sqrt{5}}.\sqrt{3+\sqrt{5}}\)

\(=3^2-\left(\sqrt{5}\right)^2\)

Answer 3

\(\sqrt{3-\sqrt{5}}.\sqrt{3+\sqrt{5}}\)

= \(\sqrt{\left(\sqrt{3-\sqrt{5}}.\sqrt{3+\sqrt{5}}\right)^2}\)

= \(\sqrt{\left(3-\sqrt{5}\right)\left(3+\sqrt{5}\right)}\)

= \(\sqrt{9-\sqrt{5}^2}\)

= \(\sqrt{9-5}=\sqrt{4}=2\)

Answer 4

=\(\sqrt{\left(3+\sqrt{5}\right).\left(3-\sqrt{5}\right)}\)

\(=9-\left(\sqrt{5}\right)^2\)

=9-5=4

-.-

Answer 5

=\(\sqrt{9-\left(\sqrt{5}\right)^2}\)

=\(\sqrt{9-5}\)

=\(\sqrt{4}=2\)