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Circles

SAT Math· difficulty 3/5

Find the radius of the circle x2+y2+10x−4y+13=0x^2 + y^2 + 10x - 4y + 13 = 0.

  • A

    44

    check_circle
  • B

    88

  • C

    1616

  • D

    13\sqrt{13}

Explanation

Complete the square: (x+5)2−25+(y−2)2−4+13=0(x+5)^2 - 25 + (y-2)^2 - 4 + 13 = 0, so (x+5)2+(y−2)2=16(x+5)^2 + (y-2)^2 = 16. Radius =4= 4.

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