Find the vertex, focus, and directrix of each parabola with the given equation. Then graph the parabola. (x + 1)2 = - 8(y + 1)
Table of contents
- 0. Review of Algebra4h 18m
- 1. Equations & Inequalities3h 18m
- 2. Graphs of Equations1h 43m
- 3. Functions2h 17m
- 4. Polynomial Functions1h 44m
- 5. Rational Functions1h 23m
- 6. Exponential & Logarithmic Functions2h 28m
- 7. Systems of Equations & Matrices4h 5m
- 8. Conic Sections2h 23m
- 9. Sequences, Series, & Induction1h 22m
- 10. Combinatorics & Probability1h 45m
8. Conic Sections
Parabolas
Problem 45
Textbook Question
Convert each equation to standard form by completing the square on x or y. Then find the vertex, focus, and directrix of the parabola. Finally, graph the parabola. y2 - 2y + 12x - 35 = 0
Verified step by step guidance1
Start by rewriting the given equation: \(y^2 - 2y + 12x - 35 = 0\). Group the \(y\) terms together and move the \(x\) term and constant to the other side: \(y^2 - 2y = -12x + 35\).
Complete the square for the \(y\) terms. Take half of the coefficient of \(y\), which is \(-2\), divide by 2 to get \(-1\), then square it to get \$1\(. Add \)1\( to both sides to maintain equality: \)y^2 - 2y + 1 = -12x + 35 + 1$.
Rewrite the left side as a perfect square: \((y - 1)^2 = -12x + 36\). Then isolate \(x\) by moving terms: \((y - 1)^2 = -12x + 36\) becomes \((y - 1)^2 = -12(x - 3)\).
Identify the vertex from the equation in standard form \((y - k)^2 = 4p(x - h)\), where the vertex is at \((h, k)\). Here, the vertex is at \((3, 1)\).
Determine the value of \(p\) by comparing \(-12\) to \$4p\(, so \)4p = -12\( which gives \)p = -3\(. Use \)p\( to find the focus at \)(h + p, k)\( and the directrix as the vertical line \)x = h - p$.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Completing the Square
Completing the square is a method used to rewrite quadratic expressions in the form (x - h)^2 or (y - k)^2 by adding and subtracting terms. This technique helps convert equations into standard form, making it easier to identify key features like the vertex of a parabola.
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Solving Quadratic Equations by Completing the Square
Standard Form of a Parabola
The standard form of a parabola's equation reveals its geometric properties clearly. For parabolas opening horizontally or vertically, the equation is written as (y - k)^2 = 4p(x - h) or (x - h)^2 = 4p(y - k), where (h, k) is the vertex and p relates to the distance between the vertex and the focus.
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Parabolas as Conic Sections
Vertex, Focus, and Directrix of a Parabola
The vertex is the parabola's turning point, the focus is a fixed point inside the parabola used to define it, and the directrix is a line perpendicular to the axis of symmetry. Knowing these helps in graphing the parabola and understanding its shape and orientation.
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Horizontal Parabolas Example 1
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