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WAEC Further Mathematics 2012 Question 11

Question 11

Coordinate Geometry

The equation of a circle is 3x2 + 3y2 + 24x − 12y = 15. Find it radius.

  1. A.2
  2. B.3
  3. C.4
  4. D.5
Show the answer and explanation

Answer: D (5)

Explanation

Divide by 3: x2 + y2 + 8x − 4y = 5, so (x + 4)2 + (y − 2)2 = 5 + 16 + 4 = 25 and r = 5.