Question:medium

If \[ \frac{d}{dx}\bigl(F(x)\bigr)=\frac{1}{e^x+1}, \] then find \(F(x)\), given that the initial condition is \[ F(0)=\log_e\!\left(\frac{1}{2}\right). \]

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An alternative trick for this integral is adding and subtracting \(e^x\) in the numerator: \[ \int \frac{1}{e^x+1}dx = \int \frac{(1+e^x) - e^x}{e^x+1}dx = \int 1 dx - \int \frac{e^x}{e^x+1}dx = x - \log_e(e^x+1) + C \] This avoids negative exponents entirely and directly yields the final functional form in seconds!
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Solution and Explanation

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