MathematicsGeometrical Applications of Complex NumbersJEE Advanced 2011Difficult
Visualized Solution (English)
Introduction to the Matching Problem
- Objective: Match Column-I statements with Column-II values.
- Key Concepts involved:
- 1. Vector Algebra: Internal angles of a triangle.
- 2. Calculus: Leibniz Rule for differentiating integrals.
- 3. Integration: Definite integral of sec(πx).
- 4. Complex Numbers: Locus and Argument of Mobius transformations.
Internal Angle of a Vector Triangle
- Given: a=(0,1,3), b=(0,−1,3), c=(0,0,23)
- Observation: a+b=c
- Angle between vectors a and b:
- cosθ=∣a∣∣b∣a⋅b=2⋅20−1+3=21⇒θ=3π
- Internal angle of triangle = π−θ=π−3π=32π
Finding f(x) using Leibniz Rule
- Equation: ∫ab(f(x)−3x)dx=a2−b2
- ∫abf(x)dx−[23x2]ab=a2−b2
- ∫abf(x)dx=21b2−21a2
- Differentiating w.r.t. b using Leibniz Rule:
- f(b)=b⇒f(x)=x
- Therefore, f(6π)=6π
Evaluating the Secant Integral
- Integral: I=∫7/65/6sec(πx)dx
- I=[π1ln∣secπx+tanπx∣]7/65/6
- At x=65: ln∣−32−31∣=ln3
- At x=67: ln∣−32+31∣=ln31
- I=π1(ln3−ln31)=π1ln3
- Final Value: ln3π2⋅π1ln3=π
Maximum Argument in Complex Plane
- Let z=eiθ=cosθ+isinθ
- w=1−z1=1−cosθ−isinθ1
- Rationalizing gives: w=21+2icot(2θ)
- Locus: Vertical line Re(w)=21
- As θ→0+, Im(w)→∞⇒Arg(w)→2π
- Maximum value of Arg(w)=2π
Final Matching Summary
- Final Match Results:
- (A) → (q): 32π
- (B) → (p): 6π
- (C) → (s): π
- (D) → (t): 2π
- Key Takeaway: Always look for geometric shortcuts in complex numbers and vector problems.
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