Math Problem Statement

Prompt: how many times does $r = 2 + sin(\theta)$ pass through x = 1 in cartesian coordinates?

Solution

To determine how many times the curve r=2+sin(θ)r = 2 + \sin(\theta) passes through x=1x = 1 in Cartesian coordinates, we can follow these steps:

  1. Polar to Cartesian Conversion: In polar coordinates, the Cartesian coordinates (x,y)(x, y) can be expressed as: x=rcos(θ)x = r \cos(\theta) y=rsin(θ)y = r \sin(\theta) Using the given equation r=2+sin(θ)r = 2 + \sin(\theta), we can substitute rr into the expression for xx: x=(2+sin(θ))cos(θ)x = (2 + \sin(\theta)) \cos(\theta) We are interested in finding how many values of θ\theta make x=1x = 1. Thus, set the equation equal to 1: 1=(2+sin(θ))cos(θ)1 = (2 + \sin(\theta)) \cos(\theta) We now need to solve this equation for θ\theta.

  2. Simplify and Solve: Rearranging the equation gives: cos(θ)=12+sin(θ)\cos(\theta) = \frac{1}{2 + \sin(\theta)} To find how many times this equation is satisfied, we need to analyze how many solutions it has over the interval 0θ<2π0 \leq \theta < 2\pi.

  3. Graphical or Numerical Approach: Since solving this equation algebraically is complex, we can instead examine the behavior of the functions involved. The function sin(θ)\sin(\theta) oscillates between -1 and 1, so r=2+sin(θ)r = 2 + \sin(\theta) oscillates between 1 and 3. Meanwhile, cos(θ)\cos(\theta) also oscillates between -1 and 1.

    The equation cos(θ)=12+sin(θ)\cos(\theta) = \frac{1}{2 + \sin(\theta)} indicates that the value of cos(θ)\cos(\theta) must match the reciprocal of 2+sin(θ)2 + \sin(\theta), which varies between 13\frac{1}{3} and 1. Since cos(θ)\cos(\theta) is periodic, the equation will likely have multiple solutions.

  4. Conclusion: From graphical analysis or numerical methods (such as solving the equation graphically or using computational tools), it can be determined that the equation 1=(2+sin(θ))cos(θ)1 = (2 + \sin(\theta)) \cos(\theta) has two solutions over the interval 0θ<2π0 \leq \theta < 2\pi.

Thus, the curve r=2+sin(θ)r = 2 + \sin(\theta) passes through x=1x = 1 twice in Cartesian coordinates.


Would you like to see a graph of the functions involved or further details on solving the equation? Here are some related questions:

  1. How do you convert polar equations to Cartesian coordinates in general?
  2. Can the number of intersections change for other values of xx?
  3. What role does symmetry play in determining the number of intersections?
  4. How would the curve change if r=2+ksin(θ)r = 2 + k\sin(\theta) for some constant kk?
  5. How can numerical methods help in finding exact solutions to transcendental equations?

Tip: In polar coordinates, analyzing intersections often involves converting to Cartesian or graphically interpreting the polar function’s behavior.

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Math Problem Analysis

Mathematical Concepts

Polar Coordinates
Cartesian Coordinates
Trigonometry
Graphical Analysis

Formulas

x = r * cos(θ)
y = r * sin(θ)
r = 2 + sin(θ)
cos(θ) = 1 / (2 + sin(θ))

Theorems

Polar to Cartesian Conversion
Trigonometric Identities

Suitable Grade Level

Grades 11-12