b, =\(\dfrac{1}{1+\sqrt{3}}+\dfrac{1}{\sqrt{3}+\sqrt{5}}\)
=\(\dfrac{\sqrt{3}+\sqrt{5}}{\left(\sqrt{3}+\sqrt{5}\right)\left(1+\sqrt{3}\right)}+\dfrac{1+\sqrt{3}}{\left(\sqrt{3}+\sqrt{5}\right)\left(1+\sqrt{3}\right)}\)
=\(\dfrac{\sqrt{3}+\sqrt{5}}{\left(\sqrt{3}+\sqrt{5}\right)\left(1+\sqrt{3}\right)}+\dfrac{1+\sqrt{3}}{\left(\sqrt{3}+\sqrt{5}\right)\left(1+\sqrt{3}\right)}\)
=\(\dfrac{2\sqrt{3}+\sqrt{5}+1}{\left(\sqrt{3}+\sqrt{5}\right)\left(1+\sqrt{3}\right)}\) (Bước nhân tích liên hợp dài quá nên bạn tự làm nha)
=\(\dfrac{-1+\sqrt{5}}{2}\)
c, \(\dfrac{a-b}{\sqrt{a}+\sqrt{b}}-\dfrac{a-2\sqrt{ab}+b}{\sqrt{a}+\sqrt{b}}\)
=\(\dfrac{a-b-a+2\sqrt{ab}-b}{\sqrt{a}+\sqrt{b}}\)
=\(\dfrac{2\sqrt{ab}-2b}{\sqrt{a}+\sqrt{b}}\)
