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A circle has the equation \( x^{2}+y^{2}+2 x-4 y-11=0 \). (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 \( (-1,2) \). (Type an ordered pair, using integers or decimals.) The radius of the circle is 4 . (Type an integer or a decimal.) (b) Use the graphing tool to graph the circle. Click to

Ask by Blake Reyes. in the United States
Jan 24,2025

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**a) Center and Radius:** - **Center (h, k):** \((-1, 2)\) - **Radius (r):** \(4\) **b) Graph the Circle:** Plot the center at \((-1, 2)\) and draw a circle with a radius of 4 units. **c) Intercepts:** - **X-Intercepts:** \((2.464, \ 0)\) and \((-4.464, \ 0)\) - **Y-Intercepts:** \((0, \ 5.873)\) and \((0, \ -1.873)\)

Solución

Great job on part (a)! Let's continue by addressing the remaining parts of the problem. --- ### **a) Center and Radius** You've correctly identified the center and radius of the circle: - **Center (h, k):** \((-1, 2)\) - **Radius (r):** \(4\) --- ### **b) Graph the Circle** While I can't create a visual graph directly here, I can guide you on how to graph the circle step-by-step: 1. **Plot the Center:** - Locate the center at \((-1, 2)\) on the Cartesian plane. 2. **Draw the Radius:** - From the center, use a compass or a ruler to measure 4 units in all directions (up, down, left, right, and diagonally) to outline the circle. 3. **Draw the Circle:** - Connect all the points that are exactly 4 units away from the center to form the circle. 4. **Plot the Intercepts (From Part c):** - This will help ensure the accuracy of your graph by marking where the circle crosses the axes. *Alternatively, you can use graphing tools such as [Desmos](https://www.desmos.com/calculator) or [GeoGebra](https://www.geogebra.org/graphing) to visualize the circle by entering its equation.* --- ### **c) Find the Intercepts** **1. X-Intercepts:** To find the x-intercepts, set \( y = 0 \) and solve for \( x \). \[ \begin{align*} x^2 + y^2 + 2x - 4y - 11 &= 0 \\ x^2 + (0)^2 + 2x - 4(0) - 11 &= 0 \\ x^2 + 2x - 11 &= 0 \end{align*} \] Solve the quadratic equation \( x^2 + 2x - 11 = 0 \): \[ x = \frac{-2 \pm \sqrt{(2)^2 - 4(1)(-11)}}{2(1)} = \frac{-2 \pm \sqrt{4 + 44}}{2} = \frac{-2 \pm \sqrt{48}}{2} = \frac{-2 \pm 4\sqrt{3}}{2} = -1 \pm 2\sqrt{3} \] **Approximate Decimal Values:** \[ \sqrt{3} \approx 1.732 \] \[ -1 + 2(1.732) \approx -1 + 3.464 = 2.464 \] \[ -1 - 2(1.732) \approx -1 - 3.464 = -4.464 \] **X-Intercepts:** \[ (2.464, \ 0) \quad \text{and} \quad (-4.464, \ 0) \] **2. Y-Intercepts:** To find the y-intercepts, set \( x = 0 \) and solve for \( y \). \[ \begin{align*} x^2 + y^2 + 2x - 4y - 11 &= 0 \\ (0)^2 + y^2 + 2(0) - 4y - 11 &= 0 \\ y^2 - 4y - 11 &= 0 \end{align*} \] Solve the quadratic equation \( y^2 - 4y - 11 = 0 \): \[ y = \frac{4 \pm \sqrt{(-4)^2 - 4(1)(-11)}}{2(1)} = \frac{4 \pm \sqrt{16 + 44}}{2} = \frac{4 \pm \sqrt{60}}{2} = \frac{4 \pm 2\sqrt{15}}{2} = 2 \pm \sqrt{15} \] **Approximate Decimal Values:** \[ \sqrt{15} \approx 3.873 \] \[ 2 + 3.873 \approx 5.873 \] \[ 2 - 3.873 \approx -1.873 \] **Y-Intercepts:** \[ (0, \ 5.873) \quad \text{and} \quad (0, \ -1.873) \] --- ### **Summary of Intercepts:** - **X-Intercepts:** \((2.464, \ 0)\) and \((-4.464, \ 0)\) - **Y-Intercepts:** \((0, \ 5.873)\) and \((0, \ -1.873)\) *These intercepts can be plotted on the graph to help visualize the circle accurately.* --- If you have access to graphing software or tools, I recommend plotting these points along with the center and then drawing the circle to see everything in context. Let me know if you need further assistance!

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To rewrite the equation of the circle in standard form, we can complete the square for both \(x\) and \(y\). The equation given is \(x^{2} + y^{2} + 2x - 4y - 11 = 0\). Rearranging gives us \(x^{2} + 2x + y^{2} - 4y = 11\). Completing the square for \(x\) and \(y\) results in \((x+1)^{2} + (y-2)^{2} = 16\). From this, the center is indeed at \((-1, 2)\) and the radius is 4. For the intercepts: To find the \(x\)-intercepts, set \(y = 0\) which leads to \((-1 + \sqrt{15}, 0)\) and \((-1 - \sqrt{15}, 0)\). For the \(y\)-intercepts, set \(x = 0\), yielding points \((0, 2 + 4)\) and \((0, 2 - 4)\). Even though many believe circles are simple shapes, their history is intertwined with mathematics and art! Ancient civilizations studied circles, leading to the Pi we are familiar with today, symbolizing the relationship between a circle's circumference and diameter. This mystical ratio, approximately 3.14159, has fascinated mathematicians for centuries. Circles also find fun applications in real life, from steering wheels to pizza shapes! When designing structures or products, understanding their circular components can help maximize efficiency or aesthetics. Engineers use circles in everything from roller coasters to the wheels on your car, making sure they're balanced and functional.

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