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Which is bigger, 8188^{18} or 18818^{8}?

8188^{18} is bigger: 8188^{18} = 1.80143 × 101610^{16} and 18818^{8} = 11019960576.

The curve ln x / x, which decides every comparison of a^b with b^a2468101214161820-0.10.10.20.30.4x = 8x = 18peak at eln x / x
The curve ln x / x, which decides every comparison of a^b with b^a. 8^18 against 18^8 is the same question as which of the two marked points is higher; the curve peaks at x = e.

How to work it out

  1. 1

    Compute both exactly: 8188^{18} = 18014398509481984 and 18818^{8} = 11019960576.

  2. 2

    So 8188^{18} is bigger.

  3. 3

    The reason: taking logs, aba^{b} against bab^{a} is the same as ln⁡aa\frac{\ln a}{a} against ln⁡bb\frac{\ln b}{b}. The function ln⁡xx\frac{\ln x}{x} rises until x=e≈2.718x = e \approx 2.718 and falls afterwards. Both 8 and 18 are past e, where the function is decreasing, so the larger exponent loses and 8188^{18} > 18818^{8}.

    ln⁡88 > ln⁡1818\frac{\ln 8}{8}\ >\ \frac{\ln 18}{18}
LaTeX source of the formulas on this page
\[ 8^{18} = 1.80143\times 10^{16}\ >\ 18^{8} = 11019960576 \]
\[ \frac{\ln 8}{8}\ >\ \frac{\ln 18}{18} \]

Questions

Which is bigger, 8188^{18} or 18818^{8}?

8188^{18} is bigger: 8188^{18} = 1.80143 × 101610^{16} and 18818^{8} = 11019960576.

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