\(\frac{4}{\sqrt{5}-1}=\frac{4\left(\sqrt{5}+1\right)}{\left(\sqrt{5}-1\right)\left(\sqrt{5}+1\right)}=\frac{4\left(\sqrt{5}+1\right)}{4}=\sqrt{5}+1\)
Chúc bạn học tốt .
=\(\frac{4\left(\sqrt{5}+1\right)}{\left(\sqrt{5}-1\right)\left(\sqrt{5}+1\right)}\)=\(\frac{4\left(\sqrt{5}+1\right)}{5-1}\)=\(\sqrt{5}+1\)