Question

Helppppp giúp e vs

Answer 1

\(\dfrac{4}{3-\sqrt{5}}-\dfrac{4}{3+\sqrt{5}}\\ =\dfrac{4\left(3+\sqrt{5}\right)}{\left(3-\sqrt{5}\right)\left(3+\sqrt{5}\right)}-\dfrac{4\left(3-\sqrt{5}\right)}{\left(3+\sqrt{5}\right)\left(3-\sqrt{5}\right)}\\ =\dfrac{4\left(3+\sqrt{5}\right)}{3^2-\left(\sqrt{5}\right)^2}-\dfrac{4\left(3-\sqrt{5}\right)}{3^2-\left(\sqrt{5}\right)^2}\\ =\dfrac{4\left(3+\sqrt{5}\right)}{9-5}-\dfrac{4\left(3-\sqrt{5}\right)}{9-5}\\ =\dfrac{4\left(3+\sqrt{5}\right)}{4}-\dfrac{4\left(3-\sqrt{5}\right)}{4}\\ =3+\sqrt{5}-3+\sqrt{5}\\ =2\sqrt{5}\)