MathematicsIntegration by SubstitutionJEE Advanced 1984Easy
Visualized Solution (English)
Understanding the Structure of ∫x2(x4+1)43dx
- Given integral: I=∫x2(x4+1)43dx
- Observe the denominator structure: a power of x outside and a binomial with a higher power of x inside a fractional power.
Factoring Out x4 from the Parentheses
- Factor out x4 from (x4+1)43:
- (x4+1)43=[x4(1+x41)]43
Simplifying the Denominator Powers
- Apply the power rule (a⋅b)n=an⋅bn:
- (x4)43⋅(1+x41)43=x3⋅(1+x41)43
- Combine with the existing x2: x2⋅x3=x5
- The integral becomes: I=∫x5(1+x41)43dx
Choosing the Substitution t=1+x41
- Let t=1+x41
- This can be written as t=1+x−4 for easier differentiation.
Differentiating to Find dt
- Differentiate t with respect to x:
- dxdt=0+(−4)x−5
- dt=−x54dx
Isolating the x5dx Term
- Rearrange to match the integral's numerator:
- x5dx=−4dt
Substituting into the Integral
- Substitute t and dt into the integral:
- I=∫t431⋅(−4dt)
- I=−41∫t−43dt
Integrating t−43 using Power Rule
- Apply the power rule ∫xndx=n+1xn+1:
- I=−41[−43+1t−43+1]+C
- I=−41[41t41]+C
Simplifying the Result
- Simplify the coefficients:
- I=−41⋅4⋅t41+C
- I=−t41+C
Final Back-substitution and Conclusion
- Substitute t=1+x41 back:
- I=−(1+x41)41+C
- Key Takeaway: Factoring out the highest power from a binomial inside a fractional power often creates a perfect substitution form.
- Next Challenge: Try evaluating ∫x3(x6+1)32dx using the same method.
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