Answer
$$\frac{\sqrt{35}}{\sqrt{21}+\sqrt{7}}=\frac{\sqrt{15}-\sqrt{5}}{2}$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}\frac{\sqrt{35}}{\sqrt{21}+\sqrt{7}}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}\frac{\sqrt{35}}{\sqrt{21}+\sqrt{7}}\frac{\sqrt{21}-\sqrt{7}}{\sqrt{21}-\sqrt{7}} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}\frac{7\sqrt{15}-7\sqrt{5}}{21-7\sqrt{3}+7\sqrt{3}-7} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}\frac{7\sqrt{15}-7\sqrt{5}}{14} \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle4}{\textcircled {4}} } }}}\frac{\sqrt{15}-\sqrt{5}}{2}\end{aligned} $$ | |
| ① | Multiply the numerator and denominator by the conjugate of the denominator . $$\color{blue}{ \sqrt{21}- \sqrt{7}} $$. |
| ② | Multiply in a numerator. $$ \color{blue}{ \sqrt{35} } \cdot \left( \sqrt{21}- \sqrt{7}\right) = \color{blue}{ \sqrt{35}} \cdot \sqrt{21}+\color{blue}{ \sqrt{35}} \cdot- \sqrt{7} = \\ = 7 \sqrt{15}- 7 \sqrt{5} $$ Simplify denominator. $$ \color{blue}{ \left( \sqrt{21} + \sqrt{7}\right) } \cdot \left( \sqrt{21}- \sqrt{7}\right) = \color{blue}{ \sqrt{21}} \cdot \sqrt{21}+\color{blue}{ \sqrt{21}} \cdot- \sqrt{7}+\color{blue}{ \sqrt{7}} \cdot \sqrt{21}+\color{blue}{ \sqrt{7}} \cdot- \sqrt{7} = \\ = 21- 7 \sqrt{3} + 7 \sqrt{3}-7 $$ |
| ③ | Simplify numerator and denominator |
| ④ | Divide both numerator and denominator by 7. |
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