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📐 Mathematics  ·  Circles & Mensuration  ·  JEE

The centre of the circle x² + y² − 4x − 6y + 9 = 0 is:

Answer: (2, 3).

  • A (2, 3)
  • B (−2, −3)
  • C (4, 6)
  • D (−4, −6)

Correct answer: A. (2, 3)

Explanation: Centre = (−g, −f) with 2g = −4, 2f = −6, giving (2, 3).

Cylinder, Cone, SphereV=πr²hCSA=2πrhV=⅓πr²hCSA=πrlV=4/3πr³SA=4πr²

Three standard 3D solids and their key formulas: a cylinder's volume scales with the full height, a cone's volume is exactly one-third of the cylinder with the same base and height, and a sphere's volume and surface area both follow distinct r-based formulas worth memorising separately.

Concept context

Perimeters, areas, and volumes of 2D and 3D shapes

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