Math Problem Statement

Find the point(s) on the surface z^2 = xy + 1 which are closest to the point (10, 8, 0).

Solution

We are tasked with finding the point(s) on the surface z2=xy+1z^2 = xy + 1 that are closest to the point (10,8,0)(10, 8, 0).

Problem breakdown:

  1. The surface is given by the equation z2=xy+1z^2 = xy + 1, which describes a relation between the coordinates (x,y,z)(x, y, z).
  2. We are trying to minimize the distance between any point (x,y,z)(x, y, z) on this surface and the point (10,8,0)(10, 8, 0).

Step 1: Distance Formula

The distance DD between a point (x,y,z)(x, y, z) on the surface and (10,8,0)(10, 8, 0) is given by the Euclidean distance formula: D=(x10)2+(y8)2+z2D = \sqrt{(x - 10)^2 + (y - 8)^2 + z^2} Since minimizing DD is equivalent to minimizing D2D^2, we can work with: D2=(x10)2+(y8)2+z2D^2 = (x - 10)^2 + (y - 8)^2 + z^2 But from the surface equation z2=xy+1z^2 = xy + 1, we can substitute z2z^2 as xy+1xy + 1. So the expression for D2D^2 becomes: D2=(x10)2+(y8)2+(xy+1)D^2 = (x - 10)^2 + (y - 8)^2 + (xy + 1) Thus, we now have the objective function: f(x,y)=(x10)2+(y8)2+xy+1f(x, y) = (x - 10)^2 + (y - 8)^2 + xy + 1 which we aim to minimize.

Step 2: Gradient and Critical Points

To minimize the function f(x,y)f(x, y), we need to find the partial derivatives with respect to xx and yy, set them to zero, and solve for xx and yy.

Let me compute that.The critical point that minimizes the distance function is (x,y)=(8,4)(x, y) = (8, 4).

Step 3: Find the corresponding zz-value

To find the zz-coordinate corresponding to this point on the surface, we substitute x=8x = 8 and y=4y = 4 into the surface equation z2=xy+1z^2 = xy + 1: z2=84+1=33z^2 = 8 \cdot 4 + 1 = 33 Thus, z=±33z = \pm \sqrt{33}.

Final Answer:

The points on the surface that are closest to (10,8,0)(10, 8, 0) are: (8,4,33)and(8,4,33)(8, 4, \sqrt{33}) \quad \text{and} \quad (8, 4, -\sqrt{33})

Do you want further details on any step, or any clarification?


Here are 5 related questions:

  1. How can we generalize this method for other surfaces?
  2. What are the second-order conditions for confirming a local minimum?
  3. What happens if the surface is defined by a different equation, such as a plane?
  4. How does this method work in higher dimensions (e.g., in 4D space)?
  5. Can the distance minimization problem be solved using Lagrange multipliers?

Tip: Minimizing the square of a distance often simplifies computations without affecting the result, as the square preserves the relative ordering of distances.

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Math Problem Analysis

Mathematical Concepts

Optimization
Partial Derivatives
Surface Equation
Distance Minimization

Formulas

Euclidean Distance Formula: D = sqrt((x - x1)^2 + (y - y1)^2 + (z - z1)^2)
Substitute surface equation: z^2 = xy + 1 into the distance formula
Objective function: f(x, y) = (x - 10)^2 + (y - 8)^2 + xy + 1

Theorems

Gradient and Critical Points
Optimization

Suitable Grade Level

Undergraduate (Calculus/Multivariable Calculus)