Math Problem Statement
Find the vertex, focus, and directrix of the following parabola. Graph the equation. x squared plus 2 x equals negative y plus 1
Solution
We are given the equation of the parabola:
Step 1: Rearrange the equation
To better analyze this equation, let's first rearrange it so that the -terms are on one side and the -terms are on the other:
Now, move the constant to the other side:
Step 2: Complete the square
To rewrite the equation in a form that reveals the vertex, we need to complete the square for the -terms. The -terms in this equation are .
- Take half of the coefficient of , which is , then square it: .
- Add and subtract this number inside the equation:
Now simplify:
So the equation becomes:
This is now in vertex form, where the vertex is at .
Step 3: Identify the vertex, focus, and directrix
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Vertex: From the equation , the vertex is .
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Focus: The equation has the general form of a parabola that opens up or down. For , the parabola opens downward because the coefficient of is negative.
The standard form of a parabola is , and the distance from the vertex to the focus is given by:
Here, , so:
Since the parabola opens downward, the focus will be at a distance of units below the vertex. The vertex is at , so the focus is at:
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Directrix: The directrix is a horizontal line located at a distance of units above the vertex. Since the vertex is at , the directrix will be the line:
Step 4: Graph the parabola
The graph will have the following characteristics:
- The vertex is at .
- The focus is at .
- The directrix is the line .
I can help you graph it, or if you'd prefer, I can generate a visual for you. Let me know!
Would you like more details on how to plot the parabola or any other aspect of this problem?
Here are some related questions:
- How do I find the vertex of a parabola from its standard equation?
- How do you find the distance to the focus and the directrix?
- What is the difference between a parabola that opens upward versus downward?
- How do you complete the square when the coefficient of is negative?
- How can I apply this to other types of parabolas (sideways or vertically shifted)?
Tip: Completing the square is a key step when dealing with quadratic equations and helps convert a general equation into vertex form, making it easier to identify the vertex, focus, and directrix.
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Math Problem Analysis
Mathematical Concepts
Algebra
Parabolas
Quadratic Equations
Vertex Form
Formulas
y = a(x - h)^2 + k
Distance to focus = 1/(4a)
Theorems
Parabola Focus and Directrix Theorem
Suitable Grade Level
Grades 9-11
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