Math Problem Statement

find the shortest distance between the parabola y=(x-5)^2 +1 and the circle x^2+y^2 = 4

Solution

To find the shortest distance between the parabola y=(x5)2+1y = (x - 5)^2 + 1 and the circle x2+y2=4x^2 + y^2 = 4, we can approach the problem using calculus and geometry. Here's a step-by-step outline:

Step 1: Understand the geometry

  • The equation y=(x5)2+1y = (x - 5)^2 + 1 represents a parabola shifted to the right by 5 units and 1 unit up.
  • The equation x2+y2=4x^2 + y^2 = 4 represents a circle centered at the origin with a radius of 2.

Our goal is to minimize the distance between any point P1=(x1,y1)P_1 = (x_1, y_1) on the parabola and any point P2=(x2,y2)P_2 = (x_2, y_2) on the circle.

Step 2: Distance formula

The distance between any two points P1=(x1,y1)P_1 = (x_1, y_1) and P2=(x2,y2)P_2 = (x_2, y_2) is given by the formula: D=(x2x1)2+(y2y1)2D = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}

We aim to minimize this distance.

Step 3: Parametrize the points on the curve

  • For the parabola y1=(x15)2+1y_1 = (x_1 - 5)^2 + 1.
  • For the circle, we parametrize the points using polar coordinates. Let: x2=2cosθ,y2=2sinθx_2 = 2 \cos \theta, \quad y_2 = 2 \sin \theta (where θ\theta is a parameter that runs around the circle).

Step 4: Set up the distance function

The distance function DD between a point P1=(x1,y1)P_1 = (x_1, y_1) on the parabola and a point P2=(x2,y2)P_2 = (x_2, y_2) on the circle becomes: D(x1,θ)=(2cosθx1)2+(2sinθ(x15)21)2D(x_1, \theta) = \sqrt{(2 \cos \theta - x_1)^2 + (2 \sin \theta - (x_1 - 5)^2 - 1)^2}

Step 5: Minimize the distance function

To find the shortest distance, we can minimize the function D(x1,θ)D(x_1, \theta) by taking partial derivatives with respect to x1x_1 and θ\theta, setting them equal to zero, and solving the resulting system of equations.

This process involves solving two simultaneous equations derived from the partial derivatives: Dx1=0andDθ=0\frac{\partial D}{\partial x_1} = 0 \quad \text{and} \quad \frac{\partial D}{\partial \theta} = 0

This step generally requires computational techniques due to the complexity of the expressions.

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Math Problem Analysis

Mathematical Concepts

Geometry
Calculus
Analytic Geometry

Formulas

Distance formula: D = sqrt((x2 - x1)^2 + (y2 - y1)^2)
Parametrization of circle: x = 2cos(θ), y = 2sin(θ)

Theorems

Optimization using partial derivatives

Suitable Grade Level

College-level Calculus or Advanced High School