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September 7th, 2015, 02:16 PM   #1
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How to find the center?

Find the center and radius of the circle with equation
x2 + y2 − 8x + 18y + 16 = 0.
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September 7th, 2015, 02:23 PM   #2
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So what is the equation of a circle with centre (X1, Y1) and radius R?

You have to manipulate the given expression to arrive at that form.

You can do this by completing the squares for (X, X1) and (Y,Y1)
or by
Multiplying out the equation for the above circle and equating coefficients.
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September 7th, 2015, 09:40 PM   #3
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Quote:
Originally Posted by studiot View Post
So what is the equation of a circle with centre (X1, Y1) and radius R?

You have to manipulate the given expression to arrive at that form.

You can do this by completing the squares for (X, X1) and (Y,Y1)
or by
Multiplying out the equation for the above circle and equating coefficients.
Ya, either complete the squares or use general form of circle. The first one is preferred as it may tell you how general form works, later you can directly use general form.
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