Chapter 11: Problem 29
Exer. 19-30: Find an equation of the parabola that satisfies the given conditions. Vertex \(V(-3,5)\), axis parallel to the \(x\)-axis, and passing through the point \((5,9)\)
Short Answer
Expert verified
The equation of the parabola is \((y - 5)^2 = 2(x + 3)\).
Step by step solution
01
Standard Form of the Parabola
We need to find the equation of a parabola with its vertex at \((-3, 5)\) and axis parallel to the \(x\)-axis. The standard form of such a parabola is \[(y - k)^2 = 4p(x - h)\]where \((h, k)\) is the vertex. Here, \(h = -3\) and \(k = 5\). Thus, the equation becomes:\[(y - 5)^2 = 4p(x + 3)\]
02
Substitute the Point into the Equation
Since the parabola passes through the point \((5, 9)\), we substitute \(x = 5\) and \(y = 9\) into the equation to find the value of \(p\):\[(9 - 5)^2 = 4p(5 + 3)\]\[(4)^2 = 4p(8)\]\[16 = 32p\]
03
Solve for p
From the equation \(16 = 32p\), solve for \(p\):\[p = \frac{16}{32} = \frac{1}{2}\]
04
Write the Equation of the Parabola
Substitute \(p = \frac{1}{2}\) back into the equation of the parabola:\[(y - 5)^2 = 4 \times \frac{1}{2}(x + 3)\]\[(y - 5)^2 = 2(x + 3)\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vertex Form of a Parabola
The vertex form of a parabola is a very informative way to express the equation of a parabola, especially when you know its vertex. The vertex form is written as:\[(y - k)^2 = 4p(x - h)\]where
- \( (h, k) \) is the vertex of the parabola, which tells us where the parabola "peaks" or "dips."
- \( p \) is a parameter that indicates the distance from the vertex to the focus of the parabola along the axis of symmetry.
Standard Form of a Parabola
The standard form of a parabola helps in writing a precise quadratic equation in a more algebraic expression. For a parabola with a horizontal orientation, as in this scenario, the standard formula is:\[(y - k)^2 = 4p(x - h)\]where
- \( (h, k) \) is the vertex.
- \( p \) is a constant dictating the parabola's "width", with its value affecting the parabola's openness.
Axis of Symmetry
The axis of symmetry of a parabola is an imaginary line that divides it into two mirror-image halves. For parabolas oriented horizontally, this axis is typically parallel to the \( x \)-axis. In the exercise, the axis was described as being parallel to the \( x \)-axis, suggesting a horizontal parabola. This line plays a crucial role because it passes through the vertex, here at \((-3, 5)\), allowing any point on the parabola to have a symmetric counterpart on the opposite side of the axis. Understanding the axis of symmetry is essential for predicting and plotting points on a parabola without solving additional equations.
Solving Quadratic Equations
Solving quadratic equations is a skill that plays into finding specific values within a parabola's equation. In the exercise, you needed to substitute a known point into the standard equation for the parabola to solve for the constant \( p \).Here's the process used:1. Substitute the \( x \) and \( y \) values of the point into the equation.2. Carefully perform algebraic manipulations to isolate \( p \).3. Solve for \( p \) to learn about the parabola's precise characteristics.In our example, substituting the point \((5, 9)\) into the equation \[(9 - 5)^2 = 4p(5 + 3)\]set up the equation \[16 = 32p\].Solving for \( p \) simplifies the problem to, \( p = \frac{1}{2} \), which could then be re-inserted into the standard equation, helping us find the exact equation for the parabola.