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WAEC Further Mathematics 2011 Question 9

Question 9

Coordinate Geometry

The equation of a circle is 3x2 + 3y2 + 6x − 12y + 6 = 0. Find its radius.

  1. A.1
  2. B.√3
  3. C.√11
  4. D.6
Show the answer and explanation

Answer: B (√3)

Explanation

Divide by 3: x2 + y2 + 2x − 4y + 2 = 0, i.e. (x + 1)2 + (y − 2)2 = 1 + 4 − 2 = 3. The radius is √3.