MathematicsVector (Cross) ProductJEE Advanced 2014Difficult
Visualized Solution (Hindi)
Introduction to Match List
- List I contains four mathematical problems from different domains.
- List II contains the possible numerical answers.
- We will solve each sub-problem (P, Q, R, S) sequentially.
Part P: Simplifying y(x)
- Given: y(x)=cos(3cos−1x)
- Let cos−1x=θ⇒x=cosθ
- Then y=cos3θ=4cos3θ−3cosθ
- Substitute x back: y=4x3−3x
Part P: Differentiation
- First derivative: dxdy=12x2−3
- Second derivative: dx2d2y=24x
Part P: Final Evaluation
- Expression: y1{(x2−1)(24x)+x(12x2−3)}
- =y1{24x3−24x+12x3−3x}
- =4x3−3x36x3−27x=4x3−3x9(4x3−3x)=9
- P matches with 4 (Value: 9)
Part Q: Regular Polygon Vectors
- Angle between consecutive vectors ak and ak+1 is θ=n2π
- ∣ak×ak+1∣=R2sin(n2π)
- ∣ak⋅ak+1∣=R2cos(n2π)
Part Q: Solving for n
- Condition: (n−1)R2sin(n2π)=(n−1)R2cos(n2π)
- ⇒tan(n2π)=1
- ⇒n2π=4π
Part Q: Minimum n
- n=8
- Q matches with 3 (Value: 8)
Part R: Ellipse and Normal
- Ellipse: 6x2+3y2=1⇒a2=6,b2=3
- Line: x+y=8 has slope m1=−1
- Normal slope mn=m1−1=1
Part R: Finding the Point
- Normal slope: b2x1a2y1=3x16y1=x12y1
- Set x12y1=1⇒x1=2y1
- Substitute into ellipse: 6(2y1)2+3y12=1⇒y12=1⇒y1=1,x1=2
Part R: Solving for h
- Normal at (2,1): 26x−13y=6−3⇒x−y=1
- Point P(h,1) lies on it: h−1=1⇒h=2
- R matches with 2 (Value: 2)
Part S: Inverse Trig Equation
- Equation: tan−12x+11+tan−14x+11=tan−1x22
- Using tan−1A+tan−1B=tan−11−ABA+B
- LHS: tan−11−(2x+1)(4x+1)12x+11+4x+11=tan−18x2+6x6x+2
Part S: Quadratic Equation
- Equate: 8x2+6x6x+2=x22⇒4x2+3x3x+1=x22
- 3x3+x2=8x2+6x⇒3x2−7x−6=0
- (3x+2)(x−3)=0
Part S: Positive Solutions
- Solutions: x=3,−32
- Only positive solution is x=3
- Number of positive solutions = 1
- S matches with 1 (Value: 1)
Final Result
- P -> 4 (9)
- Q -> 3 (8)
- R -> 2 (2)
- S -> 1 (1)
- The correct matching is (a).
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