Evaluate
91-4\sqrt{87}\approx 53.690483788
Expand
91-4\sqrt{87}
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\left(\sqrt{87}\right)^{2}-4\sqrt{87}+4
Use binomial theorem \left(a-b\right)^{2}=a^{2}-2ab+b^{2} to expand \left(\sqrt{87}-2\right)^{2}.
87-4\sqrt{87}+4
The square of \sqrt{87} is 87.
91-4\sqrt{87}
Add 87 and 4 to get 91.
\left(\sqrt{87}\right)^{2}-4\sqrt{87}+4
Use binomial theorem \left(a-b\right)^{2}=a^{2}-2ab+b^{2} to expand \left(\sqrt{87}-2\right)^{2}.
87-4\sqrt{87}+4
The square of \sqrt{87} is 87.
91-4\sqrt{87}
Add 87 and 4 to get 91.
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