Concept

Estimating Higher Roots Between Consecutive Whole Numbers

The technique used to estimate square roots can be extended to estimate higher-order roots. To estimate an nnth root like 913\sqrt[3]{91}, locate the radicand between two consecutive perfect nnth powers. Because the nnth root function preserves order, the nnth root of the number will lie between the nnth roots of those perfect powers. For instance, 9191 falls between the consecutive perfect cubes 6464 and 125125 (43=644^3 = 64 and 53=1255^3 = 125). Therefore, the cube root of 9191 must lie between 44 and 55: 4<913<54 < \sqrt[3]{91} < 5. This bounding method provides a quick numerical estimate for any root index without using a calculator.

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Updated 2026-05-01

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