Maths Olympiad Prep

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Algebra Difficulty 5.5 AIME, harder Find the answer

## Exercise 1. Calculate

321684 \sqrt{32 \sqrt{16 \sqrt{8 \sqrt{4}}}}

Only a numerical answer is expected here.

A number or a short expression. Spacing and $ signs are ignored.

Solution

## Solution to Exercise 1 We have:

321684=321682=321616=32164=3264=328=256=16\sqrt{32 \sqrt{16 \sqrt{8 \sqrt{4}}}}=\sqrt{32 \sqrt{16 \sqrt{8 \cdot 2}}}=\sqrt{32 \sqrt{16 \sqrt{16}}}=\sqrt{32 \sqrt{16 \cdot 4}}=\sqrt{32 \sqrt{64}}=\sqrt{32 \cdot 8}=\sqrt{256}=16.

Alternative Solution n1n^{\circ} 1 Using the multiplicativity of the square root, we find:

321684=3216844=42164848=42288416=821/223/822/16=821/2+3/8+1/8=8×2=16 \begin{aligned} \sqrt{32 \sqrt{16 \sqrt{8 \sqrt{4}}}} & =\sqrt{32} \cdot \sqrt[4]{16 \sqrt{8 \sqrt{4}}} \\ & =4 \sqrt{2} \cdot \sqrt[4]{16} \cdot \sqrt[8]{8 \sqrt{4}} \\ & =4 \sqrt{2} \cdot 2 \cdot \sqrt[8]{8} \cdot \sqrt[16]{4} \\ & =8 \cdot 2^{1 / 2} \cdot 2^{3 / 8} \cdot 2^{2 / 16} \\ & =8 \cdot 2^{1 / 2+3 / 8+1 / 8} \\ & =8 \times 2=16 \end{aligned}

Grader's Comment: The exercise is very well done. The few errors are due to poor manipulation of the square root.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.