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\( \leftarrow \) A circle has the equation \( x^{2}+y^{2}-3 x-6 y+9=0 \). (a) Find the center \( (h, k) \) and radius r of the circle. (b) Graph the circle. (c) Find the intercepts, if any, of the graph. (a) The center of the circle is (Type an ordered pair, using integers or fractions.)

Ask by Mills Norton. in the United States
Jan 24,2025

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Tutor-Verified Answer

Answer

The center of the circle is \(\left(\dfrac{3}{2},\ 3\right)\).

Solution

To find the center \((h, k)\) and the radius \(r\) of the circle given by the equation: \[ x^{2} + y^{2} - 3x - 6y + 9 = 0 \] we'll complete the square for both \(x\) and \(y\). ### Step 1: Rearrange the Equation Group the \(x\) terms and the \(y\) terms: \[ (x^{2} - 3x) + (y^{2} - 6y) = -9 \] ### Step 2: Complete the Square **For \(x\):** \[ x^{2} - 3x \\ = x^{2} - 3x + \left(\frac{3}{2}\right)^2 - \left(\frac{3}{2}\right)^2 \\ = \left(x - \frac{3}{2}\right)^2 - \frac{9}{4} \] **For \(y\):** \[ y^{2} - 6y \\ = y^{2} - 6y + \left(\frac{6}{2}\right)^2 - \left(\frac{6}{2}\right)^2 \\ = (y - 3)^2 - 9 \] ### Step 3: Substitute Back into the Equation \[ \left(x - \frac{3}{2}\right)^2 - \frac{9}{4} + (y - 3)^2 - 9 = -9 \] Combine like terms: \[ \left(x - \frac{3}{2}\right)^2 + (y - 3)^2 - \frac{9}{4} - 9 = -9 \] \[ \left(x - \frac{3}{2}\right)^2 + (y - 3)^2 = \frac{9}{4} \] ### Step 4: Identify the Center and Radius The equation is now in standard form: \[ \left(x - h\right)^2 + \left(y - k\right)^2 = r^2 \] Comparing, we find: - **Center \((h, k)\):** \(\left(\frac{3}{2},\ 3\right)\) - **Radius \(r\):** \(\sqrt{\frac{9}{4}} = \frac{3}{2}\) --- **Answer to Part (a):** The center of the circle is \(\left(\dfrac{3}{2},\ 3\right)\).

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Bonus Knowledge

To find the center and radius of the circle given by the equation \( x^{2}+y^{2}-3 x-6 y+9=0 \), we first rearrange the equation to standard form by completing the square. Starting with the equation: \[ x^{2}-3x + y^{2}-6y + 9 = 0 \] We can rewrite it as: \[ x^{2}-3x + y^{2}-6y = -9 \] Next, we complete the square for \( x \) and \( y \): 1. For \( x^{2}-3x \): \[ = (x - \frac{3}{2})^{2} - \frac{9}{4} \] 2. For \( y^{2}-6y \): \[ = (y - 3)^{2} - 9 \] Substituting these back into the equation gives: \[ \left( x - \frac{3}{2} \right)^{2} - \frac{9}{4} + \left( y - 3 \right)^{2} - 9 = -9 \] This simplifies to: \[ \left( x - \frac{3}{2} \right)^{2} + \left( y - 3 \right)^{2} = \frac{9}{4} \] Now we identify the center \((h, k)\) and the radius \(r\): - The center is \(\left( \frac{3}{2}, 3 \right)\) - The radius \(r\) is \(\sqrt{\frac{9}{4}} = \frac{3}{2}\) So, the center of the circle is: \[ \left( \frac{3}{2}, 3 \right) \] Now, for the intercepts: - The x-intercepts occur when \( y = 0 \): \[ \left( x - \frac{3}{2} \right)^{2} + \left( 0 - 3 \right)^{2} = \frac{9}{4} \] Solving this gives two solutions. - The y-intercepts occur when \( x = 0 \): \[ \left( 0 - \frac{3}{2} \right)^{2} + \left( y - 3 \right)^{2} = \frac{9}{4} \] Similar processing will yield the y-intercepts. Both intercepts can be calculated to find their precise values!

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