Chapter 7: Problem 54
Convert the equation from polar to rectangular form. Identify the resulting equation as a line, parabola, or circle. $$r^{2} \cos ^{2} \theta-r \sin \theta=-2$$
Short Answer
Expert verified
The rectangular form is \(x^2 - y + 2 = 0\), which represents a parabola.
Step by step solution
01
Understand the Problem
We need to convert the polar equation \(r^{2} \cos^{2} \theta - r \sin \theta = -2\) into rectangular form. In polar coordinates, \(r\) is the radial distance from the origin, and \(\theta\) is the angle. In rectangular coordinates, we use \(x\) and \(y\).
02
Use Polar-Rectangular Conversion Formulas
The conversion between polar and rectangular coordinates involves the following formulas: \(x = r \cos \theta\), \(y = r \sin \theta\), and \(r^2 = x^2 + y^2\). We will use these to convert the given equation.
03
Substitute for \(r\) and \(\theta\)
Substitute \(r \cos \theta\) with \(x\) and \(r \sin \theta\) with \(y\). First, recognize that \(\cos^2 \theta = (\frac{x}{r})^2 = \frac{x^2}{r^2}\), and substitute appropriately:\[\frac{x^2}{r^2} \cdot r^2 - r \sin \theta = -2\]
04
Simplify the Equation
Cancel \(r^2\) from the first term:\[x^2 - y = -2\]This is now in a simplified rectangular form. Rearrange to identify the form:\[x^2 - y + 2 = 0\]
05
Identify the Type of Curve
Observe the simplified equation \(x^2 - y + 2 = 0\). This equation can be rewritten as \(x^2 = y - 2\), which is a standard form of a parabola that opens upwards. The focus of the parabola is vertically above the vertex.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Polar Coordinates
Polar coordinates provide a unique way of representing points in a plane. Unlike the traditional rectangular coordinates, where every point is described by an x-coordinate and a y-coordinate, polar coordinates use a different set of information. In the polar system, a point is identified by the radial distance from the origin, denoted as \( r \), and the angle, \( \theta \), that the radial line makes with the positive x-axis.
Key features of polar coordinates include:
Key features of polar coordinates include:
- The radial distance \( r \), which tells you how far the point is from the origin. \( r \) is positive for points in the direction of \( \theta \), and negative for points in the opposite direction.
- The angle \( \theta \), measured in radians, helps in identifying the direction of the point from the origin.
Rectangular Coordinates
Rectangular coordinates, also known as Cartesian coordinates, are a way to pinpoint the exact location of a point in a two-dimensional plane using two numbers: \( x \) and \( y \). These coordinates are based on a grid-like system with two perpendicular axes, the x-axis, and the y-axis.
Important aspects of rectangular coordinates:
Important aspects of rectangular coordinates:
- The \( x \)-coordinate indicates the horizontal distance of the point from the vertical y-axis.
- The \( y \)-coordinate indicates the vertical distance of the point from the horizontal x-axis.
Parabola
A parabola is a symmetrical plane curve that is an important concept in mathematics, especially in the study of quadratic functions and conic sections. It is the set of all points equidistant from a fixed point (the focus) and a fixed straight line (the directrix).
Characteristics of a parabola:
Characteristics of a parabola:
- The vertex is the point where the curve changes direction and is the midpoint between the focus and the directrix.
- The axis of symmetry is a vertical or horizontal line that passes through the vertex, dividing the parabola into two mirror-image halves.
- The parabola can open upwards, downwards, left, or right, depending on its equation.