Math Problem Statement

What are the two main differences between the graphs of r1=3+3sintheta and r2=8+3costheta?

Solution

To compare the graphs of the polar curves r1=3+3sinθr_1 = 3 + 3\sin\theta and r2=8+3cosθr_2 = 8 + 3\cos\theta, we can analyze the following two main differences:

1. Type and Position of the Curve:

  • Curve Type:

    • r1=3+3sinθr_1 = 3 + 3\sin\theta: This equation represents a limacon with an inner loop because the coefficient of sinθ\sin\theta is equal to the constant term. The general form r=a+bsinθr = a + b\sin\theta with a=ba = b produces a limacon with an inner loop.
    • r2=8+3cosθr_2 = 8 + 3\cos\theta: This equation represents a limacon without a loop because the coefficient of cosθ\cos\theta is less than the constant term (i.e., a>ba > b). The general form r=a+bcosθr = a + b\cos\theta with a>ba > b produces a limacon without a loop.
  • Position of the Curve:

    • r1=3+3sinθr_1 = 3 + 3\sin\theta: The graph is oriented with respect to the vertical axis, because it is based on sinθ\sin\theta. The curve will be symmetric about the line θ=π2\theta = \frac{\pi}{2} (vertical axis).
    • r2=8+3cosθr_2 = 8 + 3\cos\theta: The graph is oriented with respect to the horizontal axis, because it is based on cosθ\cos\theta. The curve will be symmetric about the polar axis (horizontal axis).

2. Size and Shape of the Curve:

  • Size:

    • r1=3+3sinθr_1 = 3 + 3\sin\theta: The maximum value of r1r_1 occurs at θ=π2\theta = \frac{\pi}{2}, where r1=6r_1 = 6, and the minimum value occurs at θ=3π2\theta = \frac{3\pi}{2}, where r1=0r_1 = 0. This means the curve has a smaller overall size compared to r2r_2.
    • r2=8+3cosθr_2 = 8 + 3\cos\theta: The maximum value of r2r_2 occurs at θ=0\theta = 0, where r2=11r_2 = 11, and the minimum value occurs at θ=π\theta = \pi, where r2=5r_2 = 5. This curve is larger and does not touch the origin.
  • Shape:

    • r1=3+3sinθr_1 = 3 + 3\sin\theta: Since the curve has an inner loop (due to a=ba = b), it will have a distinctive loop near the origin.
    • r2=8+3cosθr_2 = 8 + 3\cos\theta: This curve will have a dimpled or slightly elongated shape (but no loop) and will be wider on one side, specifically extending more along the positive xx-axis (polar axis).

Summary of Differences:

  1. Type and Position:

    • r1=3+3sinθr_1 = 3 + 3\sin\theta: Limacon with an inner loop, symmetric about the vertical axis.
    • r2=8+3cosθr_2 = 8 + 3\cos\theta: Limacon without a loop, symmetric about the horizontal axis.
  2. Size and Shape:

    • r1=3+3sinθr_1 = 3 + 3\sin\theta: Smaller, with a loop near the origin.
    • r2=8+3cosθr_2 = 8 + 3\cos\theta: Larger, without a loop, dimpled shape.

Would you like more details or have any questions?

Here are five related questions to explore further:

  1. How would the graph of r1=3+3cosθr_1 = 3 + 3\cos\theta compare to r1=3+3sinθr_1 = 3 + 3\sin\theta?
  2. What happens to the graph of r2=8+3cosθr_2 = 8 + 3\cos\theta if the coefficient of cosθ\cos\theta increases?
  3. Can we classify the curve r=8+8cosθr = 8 + 8\cos\theta? What does it look like?
  4. How does the choice of sinθ\sin\theta versus cosθ\cos\theta in a polar equation affect the orientation of the graph?
  5. What is the significance of the inner loop in the limacon r1=3+3sinθr_1 = 3 + 3\sin\theta?

Tip: When analyzing polar curves, pay attention to the coefficients and their relationships—they directly affect the shape, size, and symmetry of the curve.

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Math Problem Analysis

Mathematical Concepts

Polar coordinates
Polar curves
Trigonometry

Formulas

Polar curve equations

Theorems

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Suitable Grade Level

Undergraduate level