Chapter 11: Problem 27
Find a parametric description for the given oriented curve. the directed line segment from (-2,-1) to (3,-4)the curve \(y=4-x^{2}\) from (-2,0) to (2,0) .
Short Answer
Expert verified
Line segment: \(x(t) = -2 + 5t, y(t) = -1 - 3t\) for \(t \in [0,1]\); Parabola: \(x(t) = t, y(t) = 4-t^2\) for \(t \in [-2,2]\).
Step by step solution
01
Curve Definition
First, identify the two components of the exercise. You need to express two curves parametrically: the line segment from \((-2, -1)\) to \((3, -4)\), and the parabolic section of the curve \(y=4-x^2\) from \(x = -2\) to \(x = 2\).
02
Parametric Equations for the Line Segment
The general form of a parametric equation for a line from point \((x_0, y_0)\) to point \((x_1, y_1)\) is \((x, y) = (1-t)(x_0, y_0) + t(x_1, y_1)\) for \(t\) in \([0,1]\). Substituting our points, \((-2, -1)\) and \((3, -4)\), results in:\[ x(t) = -2 + 5t \]\[ y(t) = -1 - 3t \]These equations describe the line segment from \((-2, -1)\) to \((3, -4)\).
03
Parametric Equations for the Parabola
For the parabola section, already given by \(y = 4 - x^2\), use \(x = t\) as a parameter directly, since \(x\) varies from \(-2\) to \(2\), and the equation for \(y\) remains:\[ y(t) = 4 - t^2 \]This results in parametric equations for the portion of the parabola from \((-2, 0)\) to \((2, 0)\):\[ x(t) = t, \; y(t) = 4-t^2 \]for \(t\) in \([-2, 2]\).
04
Combine both Descriptions
Summarize the parametric descriptions. For the line segment, the parametric equations are: \[ x_1(t) = -2 + 5t \]\[ y_1(t) = -1 - 3t \] for \(t\) in \([0,1]\). For the parabola, the parametric equations are: \[ x_2(t) = t, \; y_2(t) = 4-t^2 \]for \(t\) in \([-2, 2]\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Line Segment
A line segment is the shortest path between two points. In this exercise, the line segment connects the points (-2,-1) and (3,-4). It is crucial to understand that line segments are straight, and have a finite length, defined by the distance between their endpoints. When working with parametric equations for a line segment, we use a parameter, often denoted as \( t \), to smoothly transition between these endpoints.
- To describe a line segment parametrically, we identify the starting and ending points and interpolate between them.
- The general form is \((x,y) = (1-t)(x_0,y_0) + t(x_1,y_1)\)
Parabola
The concept of a parabola is fundamentally linked to its equation, which is usually of the form \( y = ax^2 + bx + c \). Here, the parabola in question is given by \( y = 4 - x^2 \). Parabolas have a characteristic symmetrical U-shape, curving upwards or downwards depending on the coefficient of the \( x^2 \) term.
- In this exercise, the parabola extends from \( x = -2 \) to \( x = 2 \).
- The vertex, or highest/lowest point, is at the origin for this parabola, with \( y = 4 \) at \( x = 0 \).
Parametric Description
Parametric description is a powerful way to represent curves, allowing the expression of both \( x \) and \( y \) coordinates as functions of a third variable, typically denoted as \( t \). This is especially useful when describing complex shapes that cannot be easily captured with a single equation in \( x \) and \( y \).
- In the context of line segments and curves, parametric equations provide flexibility by specifying movement along the path through a parameter.
- It enables us to describe orientation and direction as \( t \) typically progresses from 0 to 1 or other specified ranges.
- Changing the range of \( t \) effectively chooses different parts of the curve we want to focus on.
Oriented Curve
An oriented curve is not just a path in space but has a direction associated with it. Thus, when we speak about an oriented curve, we refer to both the line segment and the parabola, acknowledging how one moves from start to end.
- In this exercise, the orientation for the line segment describes a path from (-2,-1) to (3,-4).
- For the parabolic section, the orientation aligns with increasing \( t \), starting at \( x = -2 \) and moving through to \( x = 2 \).