Evaluate
9-4\sqrt{5}\approx 0.05572809
Expand
9-4\sqrt{5}
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\left(\sqrt{5}\right)^{2}-4\sqrt{5}+4
Use binomial theorem \left(a-b\right)^{2}=a^{2}-2ab+b^{2} to expand \left(\sqrt{5}-2\right)^{2}.
5-4\sqrt{5}+4
The square of \sqrt{5} is 5.
9-4\sqrt{5}
Add 5 and 4 to get 9.
\left(\sqrt{5}\right)^{2}-4\sqrt{5}+4
Use binomial theorem \left(a-b\right)^{2}=a^{2}-2ab+b^{2} to expand \left(\sqrt{5}-2\right)^{2}.
5-4\sqrt{5}+4
The square of \sqrt{5} is 5.
9-4\sqrt{5}
Add 5 and 4 to get 9.
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