(a) $\cos\ x\ \log\left( \frac{1 + x}{1 - x} \right)$is an odd function $\therefore\ \int_{- 1/2}^{1/2}{\cos{x\log\ \left( \frac{1 + x}{1 - x} \right)dx = 0}}$ $\therefore\ k = 0$
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Ph.D. in Physics with 19+ years of teaching experience.