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Write the equation of the circle of center eight, four and radius nine.
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The equation of any circle can be written 𝑥 minus 𝑎 all squared plus 𝑦 minus 𝑏 all squared is equal to 𝑟 squared, where the center of the circle has coordinates or ordered pair 𝑎, 𝑏 and the radius of the circle is equal to 𝑟.
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Substituting in the coordinate eight, four into the equation gives us 𝑥 minus eight all squared plus 𝑦 minus four all squared.
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As the radius of the circle is equal to nine, this will be equal to nine squared.
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Squaring nine gives us 81.
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This means that the equation of the circle is 𝑥 minus eight all squared plus 𝑦 minus four all squared equals 81.
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This is the equation of the circle with center eight, four and radius nine.