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OAU Post-UTME Mathematics 2011 Question 3

Question 3

Coordinate Geometry

Find the equation of the circle with centre (−1,3) and radius 4

  1. A.x2 + y2 − 6x + 4y = 6
  2. B.x2 + y2 + 2x − 6y = 16
  3. C.x2 + y2 − 6x + 2y = 16
  4. D.x2 + y2 + 2x − 6y = 6
Show the answer and explanation

Answer: D (x2 + y2 + 2x − 6y = 6)

Explanation

(x + 1)² + (y − 3)² = 16 expands to x² + y² + 2x − 6y + 10 = 16, i.e. x² + y² + 2x − 6y = 6.