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The center of the circle x^2 + y^2 = 18 is shifted to (2, 3). What is the new equation...

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lxsptter | Student, Undergraduate | (Level 2) Valedictorian

Posted April 29, 2013 at 3:54 AM via web

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The center of the circle x^2 + y^2 = 18 is shifted to (2, 3). What is the new equation of the circle. Please provide a graph.

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted April 29, 2013 at 4:02 AM (Answer #1)

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The general equation of a circle with center (h, k) and radius r is (x - h)^2 + (y - k)^2 = r^2.

The circle with equation x^2 + y^2 = 18 is moved so that the center lies at (2,3). The equation of the circle is now (x - 2)^2 + (y - 3)^2 = 18

=> x^2 - 4x + 4 + y^2 - 6y + 9 = 18

=> x^2 + y^2 - 4x - 6y = 5

The graph of the original circle (in black) and and that of the shifted circle (in red) is given below:

The equation of the circle after it has been shifted is: x^2 + y^2 - 4x - 6y = 5

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