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What is the value of \((\sqrt{7+\sqrt{29}}-\sqrt{7-\sqrt{29}})^2\)

A. -26
B. \(2\sqrt{29}\)
C. \(14 - 4\sqrt{5}\)
D. 14
E. \(14 + 4\sqrt{5}\)


You should apply two properties:
\((a-b)^2=a^2-2ab+b^2\);
\((a+b)(a-b)=a^2-b^2\)

\((\sqrt{7+\sqrt{29}}-\sqrt{7-\sqrt{29}})^2=(\sqrt{7+\sqrt{29}})^2-2(\sqrt{(7+\sqrt{29})(7-\sqrt{29})}+(\sqrt{7-\sqrt{29}})^2=\)
\(=7+\sqrt{29}-2\sqrt{49-29}+7-\sqrt{29}=14-2\sqrt{20}=14-4\sqrt{5}\).

Answer: C.

I've been going over this and can't seem to wrap my head around this part:

(\sqrt{7+[square_root]29}[/square_root])^2 <---- isn't this another a^2 + b^2 + 2ab? why did this reduce to just 7+\sqrt{29}?

\((\sqrt{x})^2=\sqrt{x}*\sqrt{x}=x\).

Similarly: \((\sqrt{7+\sqrt{29}})^2=\sqrt{7+\sqrt{29}}*\sqrt{7+\sqrt{29}}=7+\sqrt{29}\)
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What is the value of \((\sqrt{7+\sqrt{29}}-\sqrt{7-\sqrt{29}})^2\)

A. -26
B. \(2\sqrt{29}\)
C. \(14 - 4\sqrt{5}\)
D. 14
E. \(14 + 4\sqrt{5}\)


You should apply two properties:
\((a-b)^2=a^2-2ab+b^2\);
\((a+b)(a-b)=a^2-b^2\)

\((\sqrt{7+\sqrt{29}}-\sqrt{7-\sqrt{29}})^2=(\sqrt{7+\sqrt{29}})^2-2(\sqrt{(7+\sqrt{29})(7-\sqrt{29})}+(\sqrt{7-\sqrt{29}})^2=\)
\(=7+\sqrt{29}-2\sqrt{49-29}+7-\sqrt{29}=14-2\sqrt{20}=14-4\sqrt{5}\).

Answer: C.

I've been going over this and can't seem to wrap my head around this part:

(\sqrt{7+[square_root]29}[/square_root])^2 <---- isn't this another a^2 + b^2 + 2ab? why did this reduce to just 7+\sqrt{29}?

\((\sqrt{x})^2=\sqrt{x}*\sqrt{x}=x\).

Similarly: \((\sqrt{7+\sqrt{29}})^2=\sqrt{7+\sqrt{29}}*\sqrt{7+\sqrt{29}}=7+\sqrt{29}\)

Thanks! I see my error. Since the sq rt covers the whole (7+29), that is to be treated as one term, NOT two, so it is not A^2 + 2ab + b^2, it is just that term multiplied by itself.
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