Evaluate
9-4\sqrt{2}\approx 3.343145751
Expand
9-4\sqrt{2}
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3+4-4\sqrt{2}+\left(\sqrt{2}\right)^{2}
Use binomial theorem \left(a-b\right)^{2}=a^{2}-2ab+b^{2} to expand \left(2-\sqrt{2}\right)^{2}.
3+4-4\sqrt{2}+2
The square of \sqrt{2} is 2.
3+6-4\sqrt{2}
Add 4 and 2 to get 6.
9-4\sqrt{2}
Add 3 and 6 to get 9.
3+4-4\sqrt{2}+\left(\sqrt{2}\right)^{2}
Use binomial theorem \left(a-b\right)^{2}=a^{2}-2ab+b^{2} to expand \left(2-\sqrt{2}\right)^{2}.
3+4-4\sqrt{2}+2
The square of \sqrt{2} is 2.
3+6-4\sqrt{2}
Add 4 and 2 to get 6.
9-4\sqrt{2}
Add 3 and 6 to get 9.
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