document.write( "Question 990255: A circle passes through the Point (8,7) and touches the y-axis at the Point (0,3). Find the equation of the circle. if the circle cuts the x-axis at D and E, find the equation of another circle which is DE as diameter. \r
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Algebra.Com's Answer #610295 by josgarithmetic(39626)\"\" \"About 
You can put this solution on YOUR website!
Unknown center of the first circle, (h,k).
\n" ); document.write( "Using Distance Formula
\n" ); document.write( "\"%28h-8%29%5E2%2B%28k-7%29%5E2=%28h-0%29%5E2%2B%28k-3%29%5E2\"
\n" ); document.write( "\"%28h-8%29%5E2%2B%28k-7%29%5E2=h%5E2%2B%28k-3%29%5E2\"
\n" ); document.write( "\"h%5E2-16h%2B64%2Bk%5E2-14k%2B49=h%5E2%2Bk%5E2-6k%2B9\"
\n" ); document.write( "\"-16h%2B64-14k%2B49=-6k%2B9\"
\n" ); document.write( "\"-16h-14k%2B6k%2B64%2B49-9=0\"
\n" ); document.write( "\"-16h-8k%2B64%2B40=0\"
\n" ); document.write( "\"16h%2B8k=104\"
\n" ); document.write( "\"2h%2Bk=13\"\r
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\n" ); document.write( "\n" ); document.write( "This circle touching, just touching, the y-axis at (0,3) means that the center is some point on the line y=3. This means, you can solve for h, because you know \"k=-3\". This is based on knowing how the standard circle equation works.\r
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\n" ); document.write( "\n" ); document.write( "\"2h=13-k\"
\n" ); document.write( "\"2h=13-%28-3%29\"
\n" ); document.write( "\"2h=16\"
\n" ); document.write( "\"h=8\"\r
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\n" ); document.write( "\n" ); document.write( "Center of this first circle is therefore, (8,-3). The point (0,3) on the circle may be the convenient point to again use the Distance Formula, to find the radius of this circle.\r
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\n" ); document.write( "\n" ); document.write( "\"r%5E2=%288-0%29%5E2%2B%28-3-0%29%5E2\"
\n" ); document.write( "\"r%5E2=8%5E2\"
\n" ); document.write( "\"r=8\"\r
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\n" ); document.write( "\n" ); document.write( "This first circle equation is then, \"highlight%28%28x-8%29%5E2%2B%28y%2B3%29=8%29\".
\n" ); document.write( "I have not finished to do the final question, but maybe you can.
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