Evaluate
4\sqrt{5}+9\approx 17.94427191
Expand
4 \sqrt{5} + 9 = 17.94427191
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4+4\sqrt{5}+\left(\sqrt{5}\right)^{2}
Use binomial theorem \left(a+b\right)^{2}=a^{2}+2ab+b^{2} to expand \left(2+\sqrt{5}\right)^{2}.
4+4\sqrt{5}+5
The square of \sqrt{5} is 5.
9+4\sqrt{5}
Add 4 and 5 to get 9.
4+4\sqrt{5}+\left(\sqrt{5}\right)^{2}
Use binomial theorem \left(a+b\right)^{2}=a^{2}+2ab+b^{2} to expand \left(2+\sqrt{5}\right)^{2}.
4+4\sqrt{5}+5
The square of \sqrt{5} is 5.
9+4\sqrt{5}
Add 4 and 5 to get 9.
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