Math Problem Statement

How do I parameterize a plane through the point (3, 2, 2) with the normal vector <-2, 4, -4>?

Solution

To parameterize the plane through the point (3,2,2)(3, 2, 2) with the normal vector 2,4,4\langle -2, 4, -4 \rangle, we need to find two independent direction vectors that lie in the plane and then express the general form of a point on the plane.


Step 1: Direction vectors

The normal vector 2,4,4\langle -2, 4, -4 \rangle is orthogonal to every vector in the plane. To find two independent direction vectors, we can choose vectors perpendicular to 2,4,4\langle -2, 4, -4 \rangle.

Vector 1 (v1\mathbf{v_1}):

Let’s choose a vector v1=1,0,0\mathbf{v_1} = \langle 1, 0, 0 \rangle. Compute the dot product with 2,4,4\langle -2, 4, -4 \rangle: v12,4,4=2(1)+4(0)4(0)=20.\mathbf{v_1} \cdot \langle -2, 4, -4 \rangle = -2(1) + 4(0) - 4(0) = -2 \neq 0. This choice does not work; we need another vector.

To parameterize the plane through the point (3,2,2)(3, 2, 2) with the normal vector 2,4,4\langle -2, 4, -4 \rangle, we proceed as follows:


Step 1: Find Two Direction Vectors in the Plane

The plane's normal vector, 2,4,4\langle -2, 4, -4 \rangle, is perpendicular to all vectors lying in the plane. To find two such independent vectors, we choose vectors that are not multiples of the normal vector and satisfy the orthogonality condition:

Vector 1 (v1\mathbf{v_1}):

Choose v1=2,1,0\mathbf{v_1} = \langle 2, 1, 0 \rangle. Compute the dot product with 2,4,4\langle -2, 4, -4 \rangle: v12,4,4=(2)(2)+(4)(1)+(4)(0)=4+4+0=0.\mathbf{v_1} \cdot \langle -2, 4, -4 \rangle = (-2)(2) + (4)(1) + (-4)(0) = -4 + 4 + 0 = 0. Thus, v1=2,1,0\mathbf{v_1} = \langle 2, 1, 0 \rangle lies in the plane.

Vector 2 (v2\mathbf{v_2}):

Choose v2=0,1,1\mathbf{v_2} = \langle 0, 1, 1 \rangle. Compute the dot product with 2,4,4\langle -2, 4, -4 \rangle: v22,4,4=(2)(0)+(4)(1)+(4)(1)=0+44=0.\mathbf{v_2} \cdot \langle -2, 4, -4 \rangle = (-2)(0) + (4)(1) + (-4)(1) = 0 + 4 - 4 = 0. Thus, v2=0,1,1\mathbf{v_2} = \langle 0, 1, 1 \rangle also lies in the plane.


Step 2: Write the Parametric Equation

Using the point (3,2,2)(3, 2, 2) and the two direction vectors v1\mathbf{v_1} and v2\mathbf{v_2}, the parameterization of the plane is: r(s,t)=3,2,2+s2,1,0+t0,1,1.\mathbf{r}(s, t) = \langle 3, 2, 2 \rangle + s \langle 2, 1, 0 \rangle + t \langle 0, 1, 1 \rangle.

Simplify: r(s,t)=3+2s,2+s+t,2+t.\mathbf{r}(s, t) = \langle 3 + 2s, 2 + s + t, 2 + t \rangle.


Final Answer:

r(s,t)=3+2s,2+s+t,2+t.\mathbf{r}(s, t) = \langle 3 + 2s, 2 + s + t, 2 + t \rangle.

Let me know if you'd like a deeper explanation or additional details!


Follow-up Questions:

  1. What is the significance of choosing the two direction vectors?
  2. How can you verify that a parameterized point lies in the plane?
  3. Could the parameterization change if we chose different direction vectors?
  4. How is the normal vector related to the plane's equation?
  5. How would you find the equation of the plane in Cartesian form?

Tip:

Always double-check the orthogonality of your direction vectors with the normal vector to ensure they lie in the plane!

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Math Problem Analysis

Mathematical Concepts

Vector Calculus
Parametric Equations
Planes in 3D Geometry
Dot Product

Formulas

Dot product: \mathbf{a} \cdot \mathbf{b} = a_1b_1 + a_2b_2 + a_3b_3
Parametric equation of a plane: \mathbf{r}(s, t) = \mathbf{P_0} + s\mathbf{v_1} + t\mathbf{v_2}

Theorems

Orthogonality condition for direction vectors in the plane

Suitable Grade Level

Grades 11-12