Question
Answer
$$7\sqrt{20}^2=140$$
Explanation
Tap the blue circles to see an explanation.
| $$ \begin{aligned}7\sqrt{20}^2& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}7(2\sqrt{5})^2 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle2}{\textcircled {2}} } }}}7\cdot20 \xlongequal{ } \\[1 em] & \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle3}{\textcircled {3}} } }}}140\end{aligned} $$ | |
| ① | $$ \sqrt{20} =
\sqrt{ 2 ^2 \cdot 5 } =
\sqrt{ 2 ^2 } \, \sqrt{ 5 } =
2 \sqrt{ 5 }$$ |
| ② | $$ (2\sqrt{5})^2 =
2^{ 2 } \cdot \sqrt{5} ^ { 2 } =
2^{ 2 } \sqrt{5} ^2 =
2^{ 2 } \lvert 5 \rvert =
20 $$ |
| ③ | $ 7 \cdot 20 = 140 $ |
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