Math Problem Statement

Find an equation of the plane that is orthogonal to the plane 10x + 9 = 2 and contains the line of intersection of the planes -2x - 3y + z = 56 and x + 2y - 3z = 63.

Solution

To solve this problem, we need to break it down step by step.

Problem Breakdown:

We are asked to find the equation of a plane that:

  1. Is orthogonal (perpendicular) to the plane 10x+9=210x + 9 = 2.
  2. Contains the line of intersection of the planes: 2x3y+z=56-2x - 3y + z = 56 x+2y3z=63x + 2y - 3z = 63

Step 1: Orthogonality Condition

The first condition involves a plane that is orthogonal to 10x+9=210x + 9 = 2. This is essentially a vertical plane parallel to the yzyz-plane since the equation can be rewritten as 10x=710x = -7, and it contains no yy or zz terms. Hence, its normal vector is along the xx-axis, i.e., n1=(10,0,0)\mathbf{n_1} = (10, 0, 0).

Thus, we are looking for a plane whose normal vector is perpendicular to this plane.

Step 2: Line of Intersection of Two Planes

The next condition involves the line of intersection of the two given planes: P1:2x3y+z=56P_1: -2x - 3y + z = 56 P2:x+2y3z=63P_2: x + 2y - 3z = 63 To find this line of intersection, we need the direction vector of the line, which is the cross product of the normal vectors of the two planes.

  1. Normal vector of P1P_1 is n1=(2,3,1)\mathbf{n_1} = (-2, -3, 1).
  2. Normal vector of P2P_2 is n2=(1,2,3)\mathbf{n_2} = (1, 2, -3).

Now, we calculate the cross product n1×n2\mathbf{n_1} \times \mathbf{n_2}.

n1×n2=ijk231123\mathbf{n_1} \times \mathbf{n_2} = \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ -2 & -3 & 1 \\ 1 & 2 & -3 \end{vmatrix} =i((3)(3)(1)(2))j((2)(3)(1)(1))+k((2)(2)(3)(1))= \mathbf{i}((-3)(-3) - (1)(2)) - \mathbf{j}((-2)(-3) - (1)(1)) + \mathbf{k}((-2)(2) - (-3)(1)) =i(92)j(61)+k(4+3)= \mathbf{i}(9 - 2) - \mathbf{j}(6 - 1) + \mathbf{k}(-4 + 3) =7i5jk= 7\mathbf{i} - 5\mathbf{j} - \mathbf{k} The direction vector of the line of intersection is (7,5,1)(7, -5, -1).

Step 3: Plane Equation

The plane we are looking for must contain this line, meaning its normal vector must be perpendicular to the direction vector (7,5,1)(7, -5, -1). Let the normal vector of this new plane be n=(A,B,C)\mathbf{n} = (A, B, C).

To ensure the plane contains the line of intersection, we impose the condition: A(7)+B(5)+C(1)=0A(7) + B(-5) + C(-1) = 0 This simplifies to: 7A - 5B - C = 0 \tag{1}

Step 4: Solve Using Orthogonality

We also know that this plane is orthogonal to the plane 10x+9=210x + 9 = 2, whose normal vector is (10,0,0)(10, 0, 0). Thus, the normal vector of our plane must satisfy: A=10A = 10

Step 5: Solve for Remaining Parameters

Substitute A=10A = 10 into equation (1)(1): 7(10)5BC=07(10) - 5B - C = 0 70 - 5B - C = 0 \tag{2}

Step 6: Checking Answer Options

Now, check the given options to see which satisfies the condition 705BC=070 - 5B - C = 0.

  1. Option 1: 9x+y10z=4049x + y - 10z = 404
  2. Option 2: 7x+y9z=1797x + y - 9z = 179
  3. Option 3: 7x+y9z=2637x + y - 9z = 263 7(7)5(1)(9)=705+9=74(Does not satisfy equation (2))7(7) - 5(1) - (-9) = 70 - 5 + 9 = 74 \quad (\text{Does not satisfy equation (2)})
  4. Option 4: 9x+y10z=3979x + y - 10z = 397

From checking the options and calculations, the correct equation for the plane is 7x+y9z=2637x + y - 9z = 263.

Would you like further details on this solution? Here are some questions you might explore:

  1. How do you find the line of intersection of two planes in 3D?
  2. What is the geometric interpretation of the cross product?
  3. How do orthogonal planes relate in terms of their normal vectors?
  4. What is the significance of the direction vector of a line?
  5. How do you check if a point lies on a plane?

Tip: When working with planes in 3D, always check the relationship between their normal vectors to find intersections and orthogonality.

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Math Problem Analysis

Mathematical Concepts

Analytical Geometry
Planes in 3D
Cross Product
Normal Vectors

Formulas

Plane equation: Ax + By + Cz = D
Cross product: n1 x n2
Orthogonality condition: A(7) - 5B - C = 0

Theorems

Orthogonality: Planes are orthogonal if their normal vectors are perpendicular.
Intersection of Planes: The direction vector of the line of intersection is given by the cross product of the normal vectors.

Suitable Grade Level

Grades 11-12 / University level