“Hideous” Integral

Calculus Level 3

0 e x + e x + e e x e e e x e d x \Large \int_{0}^{\infty} e^{x+e^{x}+e^{e^{x}}-e^{e^{e^{x}}-e}} d x

If the value of the integral above can be expressed as e α e + β e i π \large e^{\alpha e+\beta e^{i \pi}} , for integers α , β \alpha, \beta , enter α + β \alpha + \beta as the answer.


The answer is 2.

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2 solutions

James Watson
Jan 5, 2021

I = 0 e x + e x + e e x e e e x e d x = e e 0 e x + e x + e e x e e e e e e x e d x \large I = \int_{0}^{\infty} e^{x+e^x+e^{e^x}-e^{e^{e^{x}}-e}}dx =e^e \int_{0}^{\infty} \orange{\frac{e^{x+e^x+e^{e^x}}}{e^e}}\cdot e^{-\blue{e^{e^{e^{x}}-e}}}dx Let u = e e e x e d u = e x + e x + e e x e e \displaystyle u = \blue{e^{e^{e^{x}}-e}} \implies du = \orange{\frac{e^{x+e^x+e^{e^x}}}{e^e}} : I = e e u = 1 u = e u d u = e e e u 1 = lim u ( e e e u ) + e e e 1 \implies I = e^e\int_{u=1}^{u=\infty}e^{-u}du = e^e\cdot -e^{-u}\bigg|_{1}^{\infty} = \lim_{u \to \infty}\left(\frac{-e^e }{e^{u}}\right) + e^e\cdot e^{-1} The limit at the front tends to 0 0 because e u e^u on the denominator tends to \infty as u u tends to \infty , leaving us with I = 0 + e e 1 = e 1 e + 1 e i π ( e i π = 1 ) I = 0 + e^{e-1} = e^{\green{1} \cdot e + \blue{1} \cdot e^{i\pi}} \; \; \; \; \; \blue{(e^{i \pi} = -1)} α + β = 1 + 1 = 2 \implies \green{\alpha} + \blue{\beta} = \green{1} + \blue{1} = \boxed{2}

This one is actually not difficult...

Clever approach with substituting e^x! Nice!

Veselin Dimov - 4 months, 4 weeks ago

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