Chapter 8: Problem 18
Find the center-radius form for each circle satisfying the given conditions. Center \((5,-1) ;\) tangent to the \(y\) -axis
Short Answer
Expert verified
\((x - 5)^2 + (y + 1)^2 = 25\)
Step by step solution
01
Identify the Circle's Center and Tangency
The center of the circle is given as \((5, -1)\). Since the circle is tangent to the \(y\)-axis, the distance from the center to the \(y\)-axis equals the radius.
02
Determine the Radius
Since the circle is tangent to the \(y\)-axis at 5 units away from \(x = 0\), the radius \(r\) must be 5 units.
03
Write the Equation in Center-Radius Form
The center-radius form of a circle is \((x-h)^2 + (y-k)^2 = r^2\), where \((h, k)\) is the center. Here, the center is \((5, -1)\) and the radius \(r = 5\). Substitute these into the equation to get:\[(x - 5)^2 + (y + 1)^2 = 25\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Center-Radius Form
The center-radius form of a circle is a very useful way to write the equation of a circle. It gives clear information about the circle's geometry. The equation looks like this:
- \((x - h)^2 + (y - k)^2 = r^2\)
- \(h\) and \(k\) are the coordinates of the circle's center,
- \(r\) is the radius of the circle.
Tangent to Axis
When a circle is tangent to an axis, it means it just touches the axis at a single point. This tangency provides useful geometric information. In our scenario, the circle is tangent to the \(y\)-axis. Since it is tangent to the \(y\)-axis, the horizontal distance from its center point to the \(y\)-axis is equal to the circle's radius. Furthermore, this implies that the circle neither crosses nor penetrates the axis at any other point.Here are a few key points to remember:
- The point of tangency occurs where the circle just touches but does not intersect the axis.
- This tangency point gives us a direct measurement of the radius, seen as the distance from the center to the axis.
- Tangency simplifies calculations since it involves straightforward distance measurements between the center and the axis.
Radius Determination
Determining the radius of a circle that is tangent to an axis can be relatively straightforward. In situations where the circle is tangent to, for example, the \(y\)-axis, the radius is simply the horizontal distance from the circle’s center to the \(y\)-axis itself.For our given example, the center of the circle is at \((5, -1)\). The \(x\)-coordinate
- 5 units away from the \(y\)-axis which means the radius is 5 units.
- The radius is a key component in constructing the circle's equation since it helps define the shape and size of the circle in relation to its center.
- Knowing the radius supports further mathematical operations and graphing tasks linked to the circle.
Equation Formulation
To formulate the equation of a circle, especially when given a center and a condition like being tangent to an axis, involves substituting known values into the center-radius form. Given the circle's center at \((5, -1)\), and radius \(5\), the formulation proceeds as follows:Start with the standard center-radius form:
- \((x-h)^2 + (y-k)^2 = r^2\)
- \((x-5)^2 + (y+1)^2 = 25\)
- Ensure correct substitution of center coordinates: \((h, k) = (5, -1)\).
- Calculate the radius square correctly: \(r^2 = 25\).
- This yields the final equation of the circle that fits the given conditions.