55016512
For each integral, choose \(u\) and \(dv\) for integration by parts. Do not evaluate the integrals.
a) \(\int xe^x\,dx\)
b) \(\int x^2\cos(x)\,dx\)
c) \(\int\ln(x)\,dx\), for \(x>0\)
Hints
- Prefer to differentiate a factor that becomes simpler.
- Choose \(dv\) so its antiderivative is immediate.
- A single logarithmic function can be treated as a product with \(1\).
Solution
1. a) Choose \(u=x\) and \(dv=e^x\,dx\). Differentiating \(x\) simplifies it, while \(e^x\) is easy to integrate.
2. b) Choose \(u=x^2\) and \(dv=\cos(x)\,dx\). Differentiating the polynomial lowers its degree.
3. c) View the integrand as \(\ln(x)\cdot1\). Choose \(u=\ln(x)\) and \(dv=dx\), because differentiating the logarithm produces \(1/x\).
Answer
a) \(u=x\), \(dv=e^x\,dx\)
b) \(u=x^2\), \(dv=\cos(x)\,dx\)
c) \(u=\ln(x)\), \(dv=dx\)
