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A circle is defined by the equation given below.

[tex]\[x^2 + y^2 - x - 2y - \frac{11}{4} = 0\][/tex]

What are the coordinates for the center of the circle and the length of the radius?

A. [tex]\(\left(\frac{1}{2}, 1\right), 4\)[/tex] units
B. [tex]\(\left(-\frac{1}{2}, -1\right), 2\)[/tex] units
C. [tex]\(\left(\frac{1}{2}, 1\right), 2\)[/tex] units
D. [tex]\(\left(-\frac{1}{2}, -1\right), 4\)[/tex] units


Sagot :

To find the center and the radius of the circle given by the equation [tex]\( x^2 + y^2 - x - 2y - \frac{11}{4} = 0 \)[/tex], we need to rewrite it in the standard form of a circle’s equation:

[tex]\[ (x - h)^2 + (y - k)^2 = r^2 \][/tex]

where [tex]\((h, k)\)[/tex] is the center of the circle and [tex]\(r\)[/tex] is the radius.

First, let's rewrite and complete the square for both [tex]\(x\)[/tex] and [tex]\(y\)[/tex] terms.

1. Completing the Square for [tex]\(x\)[/tex]:
- The terms involving [tex]\(x\)[/tex] in the equation are [tex]\(x^2 - x\)[/tex].
- To complete the square, add and subtract [tex]\((\frac{1}{2})^2\)[/tex]:
[tex]\[ x^2 - x = (x - \frac{1}{2})^2 - \frac{1}{4} \][/tex]

2. Completing the Square for [tex]\(y\)[/tex]:
- The terms involving [tex]\(y\)[/tex] in the equation are [tex]\(y^2 - 2y\)[/tex].
- To complete the square, add and subtract [tex]\(1^2\)[/tex]:
[tex]\[ y^2 - 2y = (y - 1)^2 - 1 \][/tex]

3. Rewriting the Whole Equation:
- Substitute the completed square expressions back into the original equation:
[tex]\[ (x - \frac{1}{2})^2 - \frac{1}{4} + (y - 1)^2 - 1 - \frac{11}{4} = 0 \][/tex]

4. Simplifying:
- Combine the constants on the left side:
[tex]\[ (x - \frac{1}{2})^2 + (y - 1)^2 - \frac{1}{4} - 1 - \frac{11}{4} = 0 \][/tex]
[tex]\[ (x - \frac{1}{2})^2 + (y - 1)^2 - \frac{1}{4} - 1 - \frac{11}{4} = (x - \frac{1}{2})^2 + (y - 1)^2 - \left(\frac{1}{4} + 1 + \frac{11}{4}\right) = 0 \][/tex]
[tex]\[ (x - \frac{1}{2})^2 + (y - 1)^2 - \frac{15}{4} = 0 \][/tex]
[tex]\[ (x - \frac{1}{2})^2 + (y - 1)^2 = \frac{15}{4} \][/tex]

Now the equation is in the standard form [tex]\((x - h)^2 + (y - k)^2 = r^2\)[/tex], where [tex]\(h = \frac{1}{2}\)[/tex] and [tex]\(k = 1\)[/tex], and [tex]\(r^2 = \frac{15}{4}\)[/tex].

The center [tex]\((h, k)\)[/tex] of the circle is:

[tex]\[ \left(\frac{1}{2}, 1\right) \][/tex]

The radius [tex]\(r\)[/tex] is:

[tex]\[ r = \sqrt{\frac{15}{4}} = \frac{\sqrt{15}}{2} \approx 1.2247 \][/tex]

Thus, the correct answer with the center and the radius approximately calculated is:

[tex]\[ \boxed{\left(\frac{1}{2}, 1\right), 1.22474487139159 \text{ units}} \][/tex]

The closest answer in the given options is:

[tex]\[ C. \left(\frac{1}{2}, 1\right), 2 \text{ units} \][/tex]
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