(23) Solve the equation $\ln(\frac{x-1}{x+1}) = 2$: A) $\frac{e^2+1}{e^2-1}$ B) $\frac{e^2+1}{1-e^2}$ C) $\frac{2+2e}{e-1}$ D) $\frac{2+2e}{1-e}$
(24) The divergence test cannot be used to check the convergence of:
A) $\sum_{k=1}^{\infty} 4 \cos(\pi k)$ B) $\sum_{k=1}^{\infty} \frac{k^9}{k^5-11}$ C) $\sum_{k=1}^{\infty} \frac{2k}{3k+1}$ D) $\sum_{k=1}^{\infty} \frac{1}{k^2}$
(25) Assume $f$ is a differentiable function, $\int x^3 f'(x) dx = $
A) $x^3 f(x) - \frac{1}{4} \int x^4 f(x) dx$ B) $\frac{1}{4} x^4 f(x) + c$ C) $x^3 f''(x) - 3 \int x^2 f(x) dx$ D) $x^3 f(x) - 3 \int x^2 f(x) dx$
