Math Problem Statement

Plot the points on the first circle, and find the 3 sets of polar coordinates.

Plot the point whose polar coordinates are (3, 5π/4). Find two sets of polar coordinates for the point (3, 5π/4) with the criteria: a. r > 0 and -2π ≤ θ < 0; b. r < 0 and 0 ≤ θ < 2π.

Solution

Let's go through the solution based on the given polar coordinates (3,5π4)(3, \frac{5\pi}{4}) and the instructions.

1. Plotting the Point

The point (3,5π4)(3, \frac{5\pi}{4}) in polar coordinates is given by:

  • r=3r = 3: This is the radial distance from the origin.
  • θ=5π4\theta = \frac{5\pi}{4}: This is the angle measured counterclockwise from the positive xx-axis.

To plot this point:

  • Start at the origin and move 3 units outward.
  • Locate the angle 5π4\frac{5\pi}{4}, which is in the third quadrant (it’s slightly past π\pi, or 180°).
  • Place the point 3 units out in this direction.

2. Finding Additional Polar Coordinates

Condition (a): r>0r > 0 and 2πθ<0-2\pi \leq \theta < 0

For a positive radius (r=3r = 3) and a negative angle, we can find an equivalent angle by subtracting 2π2\pi from 5π4\frac{5\pi}{4}: θ=5π42π=5π48π4=3π4\theta = \frac{5\pi}{4} - 2\pi = \frac{5\pi}{4} - \frac{8\pi}{4} = -\frac{3\pi}{4} Thus, one equivalent set of coordinates is: (3,3π4)\left( 3, -\frac{3\pi}{4} \right)

Condition (b): r<0r < 0 and 0θ<2π0 \leq \theta < 2\pi

For a negative radius, we need to reverse the direction. So, r=3r = -3. To keep the point in the same location, add π\pi to the angle 5π4\frac{5\pi}{4}: θ=5π4+π=5π4+4π4=9π4\theta = \frac{5\pi}{4} + \pi = \frac{5\pi}{4} + \frac{4\pi}{4} = \frac{9\pi}{4} Since 9π4\frac{9\pi}{4} is greater than 2π2\pi, subtract 2π2\pi to bring it back within the range [0,2π)[0, 2\pi): 9π42π=9π48π4=π4\frac{9\pi}{4} - 2\pi = \frac{9\pi}{4} - \frac{8\pi}{4} = \frac{\pi}{4} Thus, the second set of coordinates is: (3,π4)\left( -3, \frac{\pi}{4} \right)

Summary of Solutions:

  1. Original point: (3,5π4)(3, \frac{5\pi}{4})
  2. For condition (a): (3,3π4)(3, -\frac{3\pi}{4})
  3. For condition (b): (3,π4)(-3, \frac{\pi}{4})

Would you like further clarification on these steps?


Here are five related questions to deepen your understanding:

  1. How can we convert any polar coordinate with a positive radius to one with a negative radius?
  2. What are the steps for converting angles in polar coordinates between positive and negative values?
  3. How can you determine the quadrant of a point using polar coordinates?
  4. Why is subtracting 2π2\pi effective in finding equivalent angles?
  5. What is the significance of using θ=θ+π\theta = \theta + \pi when switching the sign of rr?

Tip: In polar coordinates, adding or subtracting 2π2\pi to an angle gives an equivalent point with the same position, due to the circular nature of polar coordinates.

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Math Problem Analysis

Mathematical Concepts

Polar Coordinates
Angle Conversion
Equivalent Polar Coordinates

Formulas

θ = θ ± 2π for equivalent angles
θ = θ + π to reverse radius sign

Theorems

Equivalent Angles in Polar Coordinates

Suitable Grade Level

Grades 10-12