Maths-
SAT
Easy

Question

In the xy-plane, the points (2, 4) and (-2, -4) are the endpoints of a diameter of a  circle, Which of the following is an equation of the circle?

  1. (x-2)2 +(y+4)2 = 80
  2. (x-2)2 + (y+4)2 = 20
  3. x2 + y 2 = 80
  4. x2 + y2 = 20

The correct answer is: x2 + y2 = 20


    Centre = midpoint of (2,4) & (-2, -4)
    equals open parentheses fraction numerator 2 minus 2 over denominator 2 end fraction comma fraction numerator 4 minus 4 over denominator 2 end fraction close parentheses equals left parenthesis 0 comma 0 right parenthesis
    Diameter = square root of left parenthesis 2 plus 2 right parenthesis squared plus left parenthesis 4 plus 4 right parenthesis squared end root equals square root of 4 squared plus 8 squared end root equals square root of 16 plus 64 end root equals square root of 80
    Radius = fraction numerator square root of 80 over denominator 2 end fraction equals fraction numerator 2 square root of 20 over denominator 2 end fraction equals square root of 20
    Circle equation = x2 + y2 = 20.

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