MathematicsIntegration by PartsJEE Advanced 1981Easy
Visualized Solution (Hindi)
Simplify elogx
- Identify the term elogx inside the integral.
- Apply the logarithmic identity: eloga=a.
- The expression simplifies to: x+sinx.
Distribute cosx
- Multiply the simplified expression by cosx.
- Apply the distributive property: a(b+c)=ab+ac.
- The integrand becomes: xcosx+sinxcosx.
Split the Integral
- Use the linearity property: ∫(f(x)+g(x))dx=∫f(x)dx+∫g(x)dx.
- Rewrite the problem as two separate integrals: I=∫xcosxdx+∫sinxcosxdx.
Setup Integration by Parts
- Focus on the first integral: ∫xcosxdx.
- Apply the ILATE rule to choose u and dv.
- Let u=x (Algebraic) and dv=cosxdx (Trigonometric).
Apply IBP Formula
- Use the formula: ∫udv=uv−∫vdu.
- Substitute u=x and v=∫cosxdx=sinx.
- The setup becomes: xsinx−∫sinxdx.
Integrate sinx
- Evaluate the remaining integral: ∫sinxdx=−cosx.
- Substitute back: xsinx−(−cosx).
- Result of the first part: xsinx+cosx.
Use sin2x Identity
- Focus on the second integral: ∫sinxcosxdx.
- Apply the identity: sin2x=2sinxcosx.
- Rewrite the integral as: 21∫sin2xdx.
Integrate sin2x
- Integrate sin2x using the rule: ∫sin(ax)dx=−acos(ax).
- The integral is: 21(−2cos2x).
- Result of the second part: −41cos2x.
Final Result and Takeaways
- Combine the results from both parts.
- Add the constant of integration C.
- Final Answer: xsinx+cosx−41cos2x+C.
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