Solve this with lower incomplete gamma function

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The discussion focuses on evaluating the integral ∫ e^{-\frac{2Zr}{a}} * r^{-1} dr from 0 to R using the lower incomplete gamma function. The user attempts to express the integral in terms of the gamma function but encounters an issue with divergence as the lower limit approaches zero. They note that Mathematica provides a finite result for the integral when a small positive ε is used as the lower limit, indicating that the integral diverges only when ε approaches zero. The parameters Z, a, and R are defined in relation to physical constants and variables. Understanding the behavior of the lower incomplete gamma function is crucial for resolving the divergence issue in this integral.
Alexitron
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Homework Statement


\int e^{-\frac{2Zr}{a}}*r^{-1}dr Boundaries:[0,R]




Homework Equations



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The Attempt at a Solution


I tried to solve this with lower incomplete gamma function and got \gamma(0,\frac{2ZR}{a}) which is infinite i think.
Z=81,a:Bohr radius,R=r0*A^(1/3) ,Th:A=203,r0=1,2*10^(-13)
 
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I don't know what the lower incomplete gamma function is, but Mathematica gives me
\int_\epsilon^R \frac{1}{r} e^{-2Zr/a} \, \mathrm dr = \gamma(0, 2Z\epsilon/a) - \gamma(0, 2ZR/a)
which is finite for \epsilon > 0 but diverges for \epsilon \to 0.
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

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