MathematicsEvaluation of Special Integral FormsJEE Advanced 1983Easy
Visualized Solution (Hindi)
The Integral Challenge
- Evaluate I=∫(x+1)3(x−1)exdx
- Observe the presence of ex multiplied by a rational function.
- Goal: Transform the integrand into a recognizable shortcut form.
The ex[f(x)+f′(x)] Rule
- Recall the identity: ∫ex[f(x)+f′(x)]dx=exf(x)+C
- This identity simplifies integration significantly when the derivative relationship exists.
- We need to manipulate (x+1)3x−1 to match f(x)+f′(x).
Adjusting the Numerator
- Rewrite the numerator (x−1) in terms of (x+1).
- x−1=(x+1)−2
- Substitute this back into the integral: I=∫ex[(x+1)3(x+1)−2]dx
Splitting the Fraction
- Distribute the denominator: I=∫ex[(x+1)3x+1−(x+1)32]dx
- Simplify the first fraction: (x+1)3x+1=(x+1)21
- The integral becomes: I=∫ex[(x+1)21−(x+1)32]dx
Identifying f(x) and f′(x)
- Let f(x)=(x+1)21=(x+1)−2
- Differentiate using the power rule: f′(x)=−2(x+1)−3=−(x+1)32
- The integrand is exactly in the form ex[f(x)+f′(x)], where f′(x)=−(x+1)32.
Final Result
- Using the identity ∫ex[f(x)+f′(x)]dx=exf(x)+C:
- I=ex⋅(x+1)21+C
- Final Answer: I=(x+1)2ex+C
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