5. Let C be a circle, and let P be a point not on the circle. Prove that the maximum and minimum distances from P to a point X on C occur when the line XP goes through the center of C. [Hint: Choose coordinate systems so that C is defined by x² + y? = r2 and P is a point (a, 0) on the x-axis with a ±r; use calculus to find the maximum and minimum for the square of the distance. Don't forget to pay attention to endpoints and places where a derivative might not exist.]

Algebra & Trigonometry with Analytic Geometry
13th Edition
ISBN:9781133382119
Author:Swokowski
Publisher:Swokowski
Chapter7: Analytic Trigonometry
Section7.6: The Inverse Trigonometric Functions
Problem 93E
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### Problem 5: Maximum and Minimum Distances from a Point to a Circle

**Problem Statement:**

Let \( C \) be a circle, and let \( P \) be a point not on the circle. Prove that the maximum and minimum distances from \( P \) to a point \( X \) on \( C \) occur when the line \( XP \) goes through the center of \( C \).

**Hint:** Choose coordinate systems so that \( C \) is defined by \( x^2 + y^2 = r^2 \) and \( P \) is a point \( (a,0) \) on the x-axis with \( a \neq \pm r \); use calculus to find the maximum and minimum for the square of the distance. Don’t forget to pay attention to endpoints and places where a derivative might not exist.

---

### Explanation:

1. **Choose Coordinate System:**
   - Define the circle \( C \) with the equation \( x^2 + y^2 = r^2 \).
   - Let \( P \) be the point \( (a, 0) \) on the x-axis, where \( a \neq \pm r \).

2. **Distance Formula:**
   - The square of the distance from \( P(a, 0) \) to any point \( X(x, y) \) on the circle is given by:
     \[
     D^2 = (x - a)^2 + y^2
     \]

3. **Maximize/Minimize the Distance:**
   - Substituting \( y^2 = r^2 - x^2 \) from the circle's equation:
     \[
     D^2 = (x - a)^2 + (r^2 - x^2)
     \]
   - Simplifying:
     \[
     D^2 = x^2 - 2ax + a^2 + r^2 - x^2 = a^2 - 2ax + r^2
     \]
   - To find the critical points, take the derivative of \( D^2 \) with respect to \( x \), and set it to zero:
     \[
     \frac{d(D^2)}{dx} = -2a = 0
     \]
   - Since this derivative does not have a variable part except \( -2a
Transcribed Image Text:--- ### Problem 5: Maximum and Minimum Distances from a Point to a Circle **Problem Statement:** Let \( C \) be a circle, and let \( P \) be a point not on the circle. Prove that the maximum and minimum distances from \( P \) to a point \( X \) on \( C \) occur when the line \( XP \) goes through the center of \( C \). **Hint:** Choose coordinate systems so that \( C \) is defined by \( x^2 + y^2 = r^2 \) and \( P \) is a point \( (a,0) \) on the x-axis with \( a \neq \pm r \); use calculus to find the maximum and minimum for the square of the distance. Don’t forget to pay attention to endpoints and places where a derivative might not exist. --- ### Explanation: 1. **Choose Coordinate System:** - Define the circle \( C \) with the equation \( x^2 + y^2 = r^2 \). - Let \( P \) be the point \( (a, 0) \) on the x-axis, where \( a \neq \pm r \). 2. **Distance Formula:** - The square of the distance from \( P(a, 0) \) to any point \( X(x, y) \) on the circle is given by: \[ D^2 = (x - a)^2 + y^2 \] 3. **Maximize/Minimize the Distance:** - Substituting \( y^2 = r^2 - x^2 \) from the circle's equation: \[ D^2 = (x - a)^2 + (r^2 - x^2) \] - Simplifying: \[ D^2 = x^2 - 2ax + a^2 + r^2 - x^2 = a^2 - 2ax + r^2 \] - To find the critical points, take the derivative of \( D^2 \) with respect to \( x \), and set it to zero: \[ \frac{d(D^2)}{dx} = -2a = 0 \] - Since this derivative does not have a variable part except \( -2a
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