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- 2072 Chaitra
- 2071 Shrawan · 5 marks
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- 2067 Asar
Centre, axes of ellipse 2x²+3y²−4x−12y+13=0
Short answer
Complete squares: 2(x-1)²+3(y-2)²=1. Centre (1,2); major axis length √2, minor 2/√3; eccentricity 1/√3; directrices x=1±√6/2.
Find the centre, length of axes, eccentricity and directrices of the conic (ellipse) 2x² + 3y² − 4x − 12y + 13 = 0.
Complete the squares to bring the conic to the standard form (x−h)²/a² + (y−k)²/b² = 1.
Reduction
2x² − 4x + 3y² − 12y + 13 = 0
2(x² − 2x) + 3(y² − 4y) = −13
2(x−1)² + 3(y−2)² = −13 + 2 + 12 = 1
Shift the origin to (1, 2): X = x − 1, Y = y − 2. Then
2X² + 3Y² = 1, that is X²/(1/2) + Y²/(1/3) = 1
So a² = 1/2 (major, since 1/2 > 1/3) and b² = 1/3.
Results
- Centre: (1, 2).
- Axes: major axis 2a = 2/√2 = √2 (parallel to the x-axis); minor axis 2b = 2/√3.
- Eccentricity: e² = 1 − b²/a² = 1 − (1/3)/(1/2) = 1/3, so e = 1/√3.
- Foci: ae = √(1/2) · (1/√3) = 1/√6, so the foci are (1 ± 1/√6, 2).
- Directrices: X = ±a/e = ±(1/√2)·√3 = ±√(3/2), that is x − 1 = ±√6/2, so
x = 1 ± √6/2
Check: a² − b² = 1/2 − 1/3 = 1/6 = (ae)², which matches ae = 1/√6.
✓ Answer checked by Claude Opus 5.5 (high effort)
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