document.write( "Question 39797: Write an equation of the circle whose center is at the origin and the point (3,-6) is on the circle.\r
\n" ); document.write( "\n" ); document.write( "I know the the formula to use is this:\r
\n" ); document.write( "\n" ); document.write( "(x-h)squared + (y-k)squared = r squared \n" ); document.write( "

Algebra.Com's Answer #25224 by fractalier(6550) $\"\"$ $\"About$

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Yes the equatin is correct. But the point (h, k) is the center of the circle. Here that is (0. 0).
\n" ); document.write( "But since the point (3, -6) lies on the circle, its distance from the origin is the radius of the circle.
\n" ); document.write( "Its distance is found by
\n" ); document.write( "d^2 = 3^2 + (-6)^2
\n" ); document.write( "d^2 = 9 + 36
\n" ); document.write( "d^2 = 45
\n" ); document.write( "and since d^2 is really r^2, we have
\n" ); document.write( "x^2 + y^2 = 45 \n" ); document.write( "

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