Chapter 6: Problem 1
Graph the plane curve for each pair of parametric equations by plotting points, and indicate the orientation on your graph using arrows. $$ x=3 \cos t, y=3 \sin t $$
Short Answer
Expert verified
The curve is a circle centered at the origin with radius 3, oriented counter-clockwise.
Step by step solution
01
Understand the Parametric Equations
The given parametric equations are \( x = 3 \cos t \) and \( y = 3 \sin t \). These equations describe a plane curve, where \( t \) is a parameter, typically representing an angle in radians.
02
Identify the Type of Curve
Notice that \( x = 3 \cos t \) and \( y = 3 \sin t \) resemble the parametric form of a circle. By recalling the identity \( \cos^2 t + \sin^2 t = 1 \), we can see this is a circle centered at the origin with radius 3.
03
Determine Key Points on the Curve
To graph the curve, choose values of \( t \), compute corresponding \( x \) and \( y \) values, and plot these points. For example: - \( t = 0 \), \( x = 3 \), \( y = 0 \)- \( t = \frac{\pi}{2} \), \( x = 0 \), \( y = 3 \)- \( t = \pi \), \( x = -3 \), \( y = 0 \)- \( t = \frac{3\pi}{2} \), \( x = 0 \), \( y = -3 \)- \( t = 2\pi \), \( x = 3 \), \( y = 0 \)
04
Plot the Points and Draw the Curve
Plot the points you calculated from Step 3 on a coordinate plane. Connect these points with a smooth, continuous curve to form a circle.
05
Indicate the Orientation
Since \( t \) increases, the orientation (or direction) of the curve is counter-clockwise. Indicate this by drawing arrows along the circle in a counter-clockwise direction.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Circle Graphing
When working with parametric equations like \( x = 3 \cos t \) and \( y = 3 \sin t \), an understanding of circle graphing is essential. Circle graphing involves plotting a series of points derived from equations that represent the circumference of the circle.
These parametric equations describe a circle centered at the origin with a radius of 3. Why? Because they are directly linked to the trigonometric identity \( \cos^2 t + \sin^2 t = 1 \).
Here's how it works:
These parametric equations describe a circle centered at the origin with a radius of 3. Why? Because they are directly linked to the trigonometric identity \( \cos^2 t + \sin^2 t = 1 \).
Here's how it works:
- The radius, 3, is derived from the coefficients of \( \cos t \) and \( \sin t \), both of which are multiplied by 3.
- The circle is centered at the origin \((0, 0)\) since there are no additional terms added to \( x \) or \( y \).
- This configuration represents a standard way to circle graph, making it highly predictable and systematic.
Trigonometric Functions
The use of trigonometric functions \( \cos t \) and \( \sin t \) in parametric equations is fundamental to describe the geometric path of a circle.
Trigonometric functions help express curves and cycles smoothly, thanks to their periodic nature. Here’s how they contribute:
Trigonometric functions help express curves and cycles smoothly, thanks to their periodic nature. Here’s how they contribute:
- \( \cos t \) represents the horizontal displacement. It oscillates between -1 and 1 as \( t \) increases, thus scaling horizontally by 3 in this instance, accounting for the circle's width.
- \( \sin t \) represents the vertical displacement. Similarly, it also oscillates between -1 and 1, scaled by the radius here too, allowing for movement vertically.
- Both functions complete their cycles every \( 2\pi \) radians, making them perfect for modelling circular paths since one full cycle traces a complete circle.
Plotting Points
Plotting points when dealing with parametric equations is key to constructing curves like a circle accurately. This process involves a few straightforward steps:
You begin by selecting key values of \( t \), which acts as your parameter:
To ensure that the circle is correctly traced, label and follow the orientation using arrows, typically in a counter-clockwise direction as you plot.
You begin by selecting key values of \( t \), which acts as your parameter:
- Start with \( t = 0 \). Calculate \( x = 3 \cos(0) = 3 \) and \( y = 3 \sin(0) = 0 \). This gives the point (3, 0).
- For \( t = \frac{\pi}{2} \), calculate \( x = 3 \cos(\frac{\pi}{2}) = 0 \) and \( y = 3 \sin(\frac{\pi}{2}) = 3 \). This yields the point (0, 3).
- Continue this method for \( t = \pi \), \( t = \frac{3\pi}{2} \), and \( t = 2\pi \) to complete the circle with points (-3, 0), (0, -3), and (3, 0), respectively.
To ensure that the circle is correctly traced, label and follow the orientation using arrows, typically in a counter-clockwise direction as you plot.