Evaluate
40-2\sqrt{39}\approx 27.510004003
Expand
40-2\sqrt{39}
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\left(\sqrt{39}\right)^{2}-2\sqrt{39}+1
Use binomial theorem \left(a-b\right)^{2}=a^{2}-2ab+b^{2} to expand \left(\sqrt{39}-1\right)^{2}.
39-2\sqrt{39}+1
The square of \sqrt{39} is 39.
40-2\sqrt{39}
Add 39 and 1 to get 40.
\left(\sqrt{39}\right)^{2}-2\sqrt{39}+1
Use binomial theorem \left(a-b\right)^{2}=a^{2}-2ab+b^{2} to expand \left(\sqrt{39}-1\right)^{2}.
39-2\sqrt{39}+1
The square of \sqrt{39} is 39.
40-2\sqrt{39}
Add 39 and 1 to get 40.
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