Question 12***+Verify by differentiating that \(x\sin x+\cos x+C\) is an antiderivative of \(x\cos x\).
Question 15****+Find \(a\) if \(\int x e^{ax}\,dx=e^{ax}\left(\frac{x}{a}-\frac{1}{a^2}\right)+C\) and the integrand is \(xe^{3x}\).
Question 16****+For which polynomial degree is the tabular method especially efficient in \(\int p(x)e^x\,dx\), and why?
Question 17****+Evaluate \(\int x^3 e^x\,dx\) using repeated integration by parts or the tabular pattern.
Question 18*****A student evaluating \(\int x\cos x\,dx\) writes \(x\sin x-\int\sin x\,dx=x\sin x-\cos x+C\). Find and correct the sign error.
Question 19*****Explain why choosing \(u=e^x\) and \(dv=x\,dx\) is inefficient for \(\int xe^x\,dx\), even though it is not illegal.