Skip to content
Question of 373

Q.Evaluate ∫xsin⁡3x dx\int x \sin 3x \, dx.

Karnataka PUCKarnataka II PUC Board 2023Subjective· 3mImportance★★★★★
0% · 0/373 Questions
🔒 Locked · start free trial →

You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.

Start your 14-day free trial to unlock the full solution →

Apply integration by parts (u=xu=x, dv=sin⁡3x dxdv=\sin 3x\,dx) to obtain −x3cos⁡3x+19sin⁡3x+C-\frac{x}{3}\cos 3x+\frac{1}{9}\sin 3x+C.

Step 1 — Choose parts. Using ∫u dv=uv−∫v du\int u\,dv=uv-\int v\,du, take

u=x (⇒du=dx),dv=sin⁡3x dx ⇒ v=−13cos⁡3x.u=x\ (\Rightarrow du=dx),\qquad dv=\sin 3x\,dx\ \Rightarrow\ v=-\frac13\cos 3x.

Step 2 — Apply the formula.

∫xsin⁡3x dx=x(−13cos⁡3x)−∫(−13cos⁡3x)dx=−x3cos⁡3x+13∫cos⁡3x dx.\int x\sin 3x\,dx=x\left(-\frac13\cos 3x\right)-\int\left(-\frac13\cos 3x\right)dx=-\frac{x}{3}\cos 3x+\frac13\int\cos 3x\,dx.

Step 3 — Integrate the remaining term.

∫cos⁡3x dx=13sin⁡3x,\int\cos 3x\,dx=\frac13\sin 3x,

so …

Unlock everything free for 14 days

  • Full step-by-step solutions
  • Concept-first explanations
  • Methods, shortcuts & mistakes
  • PYQ mapping + timed mock tests

Full access for 14 days. No credit card required.