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To evaluate $\int x\cos x\, dx$, the best technique is:
ADirect substitution $u = \cos x$ on the chart at one step
BPartial fractions, since the integrand is a rational function
CTrigonometric identity simplification on the school chart
DIntegration by parts with $u = x$, $dv = \cos x\, dx$
Answer & Solution
Correct answer: D. Integration by parts with $u = x$, $dv = \cos x\, dx$
Integration by parts: $u = x$, $dv = \cos x\, dx$ gives $du = dx$, $v = \sin x$; result $x\sin x + \cos x + C$.
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