InfiniteRepitition Intermediate
2002


Problem - 3276
Write $\sqrt[3]{2+5\sqrt{3+2\sqrt{2}}}$ in the form of $a+b\sqrt{2}$ where $a$ and $b$ are integers.

Firstly, $$\sqrt[3]{2+5\sqrt{3+2\sqrt{2}}}=\sqrt[3]{2+5(1+\sqrt{2})}=\sqrt[3]{7+5\sqrt{2}}$$ Now, $$(a+b\sqrt{2})^3 = (a^3+6ab^2) + (3a^2b + 2b^3)\sqrt{2}$$ Hence $$ \left\{ \begin{array}{} a^3 + 6ab^2 &=7\\ 3a^2 + 2b^3 &=5 \end{array} \right. \implies (a, b) = (1, 1) $$ $$\therefore\quad \sqrt[3]{2+5\sqrt{3+2\sqrt{2}}} =\boxed{1+\sqrt{2}}$$

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