Tính giá trị biểu thức $\frac{2}{\sqrt{7} -\sqrt{5} }$ -$\frac{1}{3}$$\sqrt{63}+$ $\frac{1}{4}$ $\sqrt{20}$ 05/07/2021 Bởi Rose Tính giá trị biểu thức $\frac{2}{\sqrt{7} -\sqrt{5} }$ -$\frac{1}{3}$$\sqrt{63}+$ $\frac{1}{4}$ $\sqrt{20}$
$\frac{2}{\sqrt{7}-\sqrt{5}}-\frac{1}{3}\sqrt{63}+\frac{1}{4}\sqrt{20}$ $=\frac{2(\sqrt{7}+\sqrt{5})}{(\sqrt{7}-\sqrt{5})(\sqrt{7}+\sqrt{5})}-\frac{1}{3}.3\sqrt{7}+\frac{1}{4}.2\sqrt{5}$ $=\frac{2(\sqrt{7}+\sqrt{5})}{7-5}-\sqrt{7}+\frac{\sqrt{5}}{2}$ $=\frac{2(\sqrt{7}+\sqrt{5})}{2}-\sqrt{7}+\frac{\sqrt{5}}{2}$ $=\sqrt{7}+\sqrt{5}-\sqrt{7}+\frac{\sqrt{5}}{2}$ $=\frac{3\sqrt{5}}{2}$ Bình luận
`frac{2}{\sqrt{7}-\sqrt{5}}-1/3\sqrt{63}+1/4\sqrt{20}` `=frac{2(\sqrt{7}+\sqrt{5})}{(\sqrt{7}-\sqrt{5})(\sqrt{7}+\sqrt{5})}-\sqrt{7}+frac{\sqrt{5}}{2}` `=frac{2(\sqrt{7}+\sqrt{5})}{7-5}-\sqrt{7}+frac{\sqrt{5}}{2}` `=\sqrt{7}+\sqrt{5}-\sqrt{7}+frac{\sqrt{5}}{2}` `=\sqrt{5}+frac{\sqrt{5}}{2}` `=frac{3\sqrt{5}}{2}` Bình luận
$\frac{2}{\sqrt{7}-\sqrt{5}}-\frac{1}{3}\sqrt{63}+\frac{1}{4}\sqrt{20}$
$=\frac{2(\sqrt{7}+\sqrt{5})}{(\sqrt{7}-\sqrt{5})(\sqrt{7}+\sqrt{5})}-\frac{1}{3}.3\sqrt{7}+\frac{1}{4}.2\sqrt{5}$
$=\frac{2(\sqrt{7}+\sqrt{5})}{7-5}-\sqrt{7}+\frac{\sqrt{5}}{2}$
$=\frac{2(\sqrt{7}+\sqrt{5})}{2}-\sqrt{7}+\frac{\sqrt{5}}{2}$
$=\sqrt{7}+\sqrt{5}-\sqrt{7}+\frac{\sqrt{5}}{2}$
$=\frac{3\sqrt{5}}{2}$
`frac{2}{\sqrt{7}-\sqrt{5}}-1/3\sqrt{63}+1/4\sqrt{20}`
`=frac{2(\sqrt{7}+\sqrt{5})}{(\sqrt{7}-\sqrt{5})(\sqrt{7}+\sqrt{5})}-\sqrt{7}+frac{\sqrt{5}}{2}`
`=frac{2(\sqrt{7}+\sqrt{5})}{7-5}-\sqrt{7}+frac{\sqrt{5}}{2}`
`=\sqrt{7}+\sqrt{5}-\sqrt{7}+frac{\sqrt{5}}{2}`
`=\sqrt{5}+frac{\sqrt{5}}{2}`
`=frac{3\sqrt{5}}{2}`