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WAEC 2020 · Paper 1 · Q24

A circle with centre (5,−4)(5, -4) passes through the point (5,0)(5, 0). Find its equation.

Worked solution (try it first)
  1. The radius is the distance from (5,−4)(5, -4) to (5,0)(5, 0), which is 44.
  2. So the circle is (x−5)2+(y+4)2=16(x - 5)^2 + (y + 4)^2 = 16.
  3. Expand: x2−10x+25+y2+8y+16=16x^2 - 10x + 25 + y^2 + 8y + 16 = 16.
  4. Subtract 16: x2+y2−10x+8y+25=0x^2 + y^2 - 10x + 8y + 25 = 0, option C.

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