Math Problem Statement

Convert the following polar equation into a rectangular equation. If possible, write the rectangular equation with y as a function of x. r = 1 - 2 cos(θ) (Hint: Eliminate any radicals in your equation.)

Solution

To convert the given polar equation r=12cos(θ)r = 1 - 2 \cos(\theta) into rectangular form, we use the relationships between polar and rectangular coordinates:

x=rcos(θ),y=rsin(θ),r2=x2+y2,cos(θ)=xr.x = r \cos(\theta), \quad y = r \sin(\theta), \quad r^2 = x^2 + y^2, \quad \cos(\theta) = \frac{x}{r}.

Step-by-Step Solution:

  1. Substitute cos(θ)=xr\cos(\theta) = \frac{x}{r} into the polar equation: r=12cos(θ).r = 1 - 2 \cos(\theta). Replacing cos(θ)\cos(\theta) gives: r=12(xr).r = 1 - 2 \left( \frac{x}{r} \right).

  2. Eliminate the fraction by multiplying through by rr: r2=r2x.r^2 = r - 2x.

  3. Replace r2r^2 with x2+y2x^2 + y^2: x2+y2=r2x.x^2 + y^2 = r - 2x.

  4. Solve for rr: Recall r=x2+y2r = \sqrt{x^2 + y^2}, so substitute rr back: x2+y2=x2+y22x.x^2 + y^2 = \sqrt{x^2 + y^2} - 2x.

  5. Square both sides to eliminate the square root: (x2+y2)2=(x2+y22x)2.(x^2 + y^2)^2 = \left( \sqrt{x^2 + y^2} - 2x \right)^2.

    Expand the right-hand side using (ab)2=a22ab+b2(a - b)^2 = a^2 - 2ab + b^2: (x2+y2)2=(x2+y2)24xx2+y2+4x2.(x^2 + y^2)^2 = (\sqrt{x^2 + y^2})^2 - 4x\sqrt{x^2 + y^2} + 4x^2.

    Simplify further: (x2+y2)2=x2+y24xx2+y2+4x2.(x^2 + y^2)^2 = x^2 + y^2 - 4x\sqrt{x^2 + y^2} + 4x^2.

  6. Simplify and rearrange: Combine like terms: (x2+y2)2x2y24x2=4xx2+y2.(x^2 + y^2)^2 - x^2 - y^2 - 4x^2 = -4x\sqrt{x^2 + y^2}.

This is the rectangular equation. You may leave the result in this implicit form since solving explicitly for yy as a function of xx is generally complicated.


Summary:

The rectangular form of the given polar equation r=12cos(θ)r = 1 - 2 \cos(\theta) simplifies to: (x2+y2)2=(x2+y2)4xx2+y2+4x2.(x^2 + y^2)^2 = (x^2 + y^2) - 4x\sqrt{x^2 + y^2} + 4x^2.

Would you like a detailed explanation of any step? Let me know if you'd like to focus on simplifying further or any clarifications!


Related Questions:

  1. How do you convert r=1+2sin(θ)r = 1 + 2 \sin(\theta) to rectangular form?
  2. What is the relationship between polar and rectangular coordinates?
  3. How do you plot r=12cos(θ)r = 1 - 2 \cos(\theta) on a polar graph?
  4. Can you derive cos(θ)\cos(\theta) and sin(θ)\sin(\theta) using xx and yy?
  5. How do you handle square roots when converting polar equations?

Tip: When converting between polar and rectangular forms, start with the key relationships r2=x2+y2r^2 = x^2 + y^2 and cos(θ)=xr\cos(\theta) = \frac{x}{r}.

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Math Problem Analysis

Mathematical Concepts

Polar to Rectangular Conversion
Coordinate Geometry
Algebraic Manipulations

Formulas

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

Theorems

Relationship between Polar and Cartesian Coordinates

Suitable Grade Level

Grades 10-12