HP Prime & HP 49G Problem with square roots
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06-26-2014, 05:58 PM
(This post was last modified: 06-26-2014 07:06 PM by Manolo Sobrino.)
Post: #10
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RE: HP Prime & HP 49G Problem with square roots
OK, first let's notice that 1201 is prime, 42035=35*1201 and 1236=35+1201. Now rewrite the longer expression:
\begin{equation} \sqrt{35+2\sqrt{6}}+\sqrt{1201+35-2\sqrt{6}+2\sqrt{\left(35-2\sqrt{6}\right)1201}} \end{equation} That is the square of a sum:\begin{equation} \sqrt{35+2\sqrt{6}}+\sqrt{\left(\sqrt{1201}+\sqrt{35-2\sqrt{6}}\right)^2} \end{equation} You don't need to worry about the absolute value, it's simply:\begin{equation}\sqrt{1201}+\sqrt{35+2\sqrt{6}}+\sqrt{35-2\sqrt{6}} \end{equation} If a>b it's trivial to prove that:\begin{equation}\sqrt{a+b}+\sqrt{a-b}=\sqrt{2a+2\sqrt{a^2-b^2}}\end{equation} In this case: \begin{equation}\sqrt{70+2\sqrt{1225-4\cdot 6}}=\sqrt{70+2\sqrt{1201}}\end{equation} There you go. (You guys should use paper and pencil more often ) |
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