document.write( "Question 167715: How would I complete the square for both x and y and find the equation of the circle for the given equation x^2-8x+y^2+4y-205=0. I also have the same question for the following equation x^2+12x+y^2-14y-204=0. \n" ); document.write( "
Algebra.Com's Answer #123626 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
I'll do the first (which hopefully will help you do the second)\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "# 1\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x%5E2-8x%2By%5E2%2B4y-205=0\" Start with the given equation\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x%5E2-8x%2By%5E2%2B4y=%2B205\" Add \"205\" to both sides\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"%28x-4%29%5E2-16%2By%5E2%2B4y=205\" Complete the square for the \"x\" terms. Note: Let me know if you need help completing the square.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"%28x-4%29%5E2-16%2B%28y%2B2%29%5E2-4=205\" Complete the square for the \"y\" terms\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"%28x-4%29%5E2%2B%28y%2B2%29%5E2-20=205\" Combine like terms\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"%28x-4%29%5E2%2B%28y%2B2%29%5E2=205%2B20\" Add \"20\" to both sides\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"%28x-4%29%5E2%2B%28y%2B2%29%5E2=225\" Combine like terms\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "-----------\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Notice how the equation is now in the form \"%28x-h%29%5E2%2B%28y-k%29%5E2=r%5E2\". This means that this conic section is a circle where (h,k) is the center and \"r\" is the radius.\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "So the circle has these properties:\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Center: (4,-2)\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Radius: \"r=sqrt%28225%29=15\"
\n" ); document.write( "
\n" );