Chapter 11: Problem 20
Graph the sets of points whose polar coordinates satisfy the equations and inequalities in Exercises \(11-26 .\) $$\theta=\pi / 2, \quad r \leq 0$$
Short Answer
Expert verified
Points are located along the negative y-axis.
Step by step solution
01
Convert Polar to Cartesian
In polar coordinates, the angle \(\theta\) represents the angle from the positive x-axis. When \(\theta = \pi/2\), this corresponds to the positive y-direction. We need to find the set of points that lie along the angle line where \(r \leq 0\).
02
Analyze the Constraint on r
The inequality \(r \leq 0\) means that we consider points that lie on the same line but in the direction opposite to the typical direction given by \(\theta = \pi/2\). These are negative radial distances, so they lie on the line where \(\theta = 3\pi/2\) in standard polar convention, which corresponds to the negative y-axis.
03
Graph the Points
To graph these points, draw a vertical line at \(\theta = \pi/2\) which is the positive y-axis. Then choose the opposite side (or direction) for negative distances, so draw actually in the negative direction of this, which is the negative y-axis. Since \(r \leq 0\), the line should have an arrow indicating direction towards negative y-axis, starting from the origin downward indefinitely.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Graphing Polar Equations
In the realm of polar coordinates, graphing is a way of representing equations that are defined using the distance from the origin and the angle from the positive x-axis. Unlike Cartesian coordinates, polar plots involve a circle with an angle, \( \theta \), which rotates from the positive x-axis to locate points along the edge. The other component, the radial distance \( r \), extends outward or inward along this angle, forming various shapes and lines.
- First, identify the angle \( \theta \) involved in the equation. Here, \( \theta = \pi/2 \) signifies a line vertical to the x-axis, typically positive y.
- Next, interpret the radial distance \( r \), which determines how far from or towards the origin a point lies on the defined angle line.
- Finally, plot the graph by following these directions, which might include traditional and non-traditional plotting lines, like the negative y-axis in this exercise.
Cartesian Conversion
Converting between polar and Cartesian systems is a fundamental aspect of working with coordinates, ensuring that calculations and visualizations can be cross-verified between xy-planes and angle-radial models. This conversion allows one to transition a polar coordinate \((r, \theta)\) into familiar planes.
- For a given polar coordinate \((r, \theta)\), the Cartesian x-coordinate is given by \( x = r \cos(\theta) \).
- The y-coordinate follows as \( y = r \sin(\theta) \).
- Using these formulas, one can seamlessly convert any polar equation into Cartesian contexts, and vice versa.
Negative Radial Distances
In polar coordinates, radial distances can be either positive or negative, a feature that significantly influences how certain values and lines are graphed. Understanding this unusual aspect is crucial for precise representations.
- A positive \( r \) suggests points along the direction of \( \theta \) from the origin moving outward, commonly shown as the area ahead of the origin.
- Conversely, a negative \( r \) implies points along the same angle but moving inward or behind the origin's line. This is akin to reflecting the line across the origin.
- This concept is illustrated in the problem at hand, where \( r \leq 0 \) results in graphing along the opposite direction of \( \theta = \pi/2 \), marking locations on the negative y-axis instead of the positive side.