MathematicsSolving Inverse Trigonometric EquationsJEE Advanced 2007Moderate
Visualized Solution (English)
Analyze the Equation
- Given equation: sin−1(ax)+cos−1(y)+cos−1(bxy)=2π
- Rearrange to isolate the cosine terms: cos−1(y)+cos−1(bxy)=2π−sin−1(ax)
Apply Complementary Identity
- Using identity: 2π−sin−1(θ)=cos−1(θ)
- Equation becomes: cos−1(y)+cos−1(bxy)=cos−1(ax)
Trigonometric Substitution
- Let α=cos−1y, β=cos−1(bxy), and γ=cos−1(ax)
- Then α+β=γ⟹β=γ−α
- Taking cosine on both sides: cosβ=cos(γ−α)
Expand and Substitute Back
- Expansion: cosβ=cosγcosα+sinγsinα
- Substitute back: bxy=(ax)(y)+1−a2x21−y2
Isolate the Radical and Square
- Isolate root: (b−a)xy=1−a2x21−y2
- Square both sides: (b−a)2x2y2=(1−a2x2)(1−y2)
Case A: a=1,b=0
- Substitute a=1,b=0: (0−1)2x2y2=(1−x2)(1−y2)
- x2y2=1−x2−y2+x2y2
- Result: x2+y2=1 (Matches statement p)
Case B: a=1,b=1
- Substitute a=1,b=1: (1−1)2x2y2=(1−x2)(1−y2)
- 0=(1−x2)(1−y2)
- Result: (x2−1)(y2−1)=0 (Matches statement q)
Case C: a=1,b=2
- Substitute a=1,b=2: (2−1)2x2y2=(1−x2)(1−y2)
- x2y2=1−x2−y2+x2y2
- Result: x2+y2=1 (Matches statement p)
Case D: a=2,b=2
- Substitute a=2,b=2: (2−2)2x2y2=(1−4x2)(1−y2)
- 0=(1−4x2)(1−y2)
- Result: (4x2−1)(y2−1)=0 (Matches statement s)
Final Summary
- Key Takeaways:
- Identity sin−1θ+cos−1θ=2π is powerful for simplification.
- Squaring is necessary to remove radicals but can introduce extraneous solutions; always check constraints.
- Final Match:
- A → p; B → q; C → p; D → s
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