Chapter 11: Problem 21
Find the equation of the plane through \((6,2,-1)\) and perpendicular to the line of intersection of the planes \(4 x-3 y+2 z+5=0\) and \(3 x+2 y-z+11=0\).
Short Answer
Expert verified
The plane's equation is \(-x + 10y + 17z + 3 = 0\).
Step by step solution
01
Find the Normal Vector of the Given Planes
The normal vector of the plane \(4x - 3y + 2z + 5 = 0\) is \(\mathbf{n_1} = (4, -3, 2)\), and the normal vector of the plane \(3x + 2y - z + 11 = 0\) is \(\mathbf{n_2} = (3, 2, -1)\).
02
Cross Product for Line of Intersection Normal
The line of intersection of the planes is perpendicular to both normal vectors \(\mathbf{n_1}\) and \(\mathbf{n_2}\). Therefore, find the cross product \(\mathbf{n} = \mathbf{n_1} \times \mathbf{n_2}\).\[\mathbf{n} = \begin{vmatrix}\mathbf{i} & \mathbf{j} & \mathbf{k} \4 & -3 & 2 \3 & 2 & -1\end{vmatrix}\]\(\mathbf{n} = ((-3)(-1) - (2)(2)) \mathbf{i} - ((4)(-1) - (2)(3)) \mathbf{j} + ((4)(2) - (-3)(3)) \mathbf{k}\)\(\mathbf{n} = (3 - 4)\mathbf{i} - (-4 - 6)\mathbf{j} + (8 + 9)\mathbf{k}\)\(\mathbf{n} = (-1, 10, 17)\).
03
Equation of the Plane Through Given Point
Now we have a point \((6, 2, -1)\) and a normal vector \((-1, 10, 17)\). The equation of a plane can be written as:\[a(x - x_0) + b(y - y_0) + c(z - z_0) = 0\]Substitute \(a = -1\), \(b = 10\), \(c = 17\), and the point \((x_0, y_0, z_0) = (6, 2, -1)\):\[-1(x - 6) + 10(y - 2) + 17(z + 1) = 0\]Simplifying, this becomes:\[-x + 6 + 10y - 20 + 17z + 17 = 0\]So, the equation is:\[-x + 10y + 17z + 3 = 0\].
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Understanding the Cross Product
The cross product is a mathematical operation that is highly useful when dealing with vectors, especially in three dimensions. It allows you to find a vector that is perpendicular to two given vectors. In this context, the cross product of the normal vectors from the original planes provides a directional vector that is perpendicular to both. The formula for the cross product can be expressed as:
- If you have two vectors, \( \mathbf{a} = (a_1, a_2, a_3) \) and \( \mathbf{b} = (b_1, b_2, b_3) \), their cross product is given by:\[\mathbf{a} \times \mathbf{b} = (a_2b_3 - a_3b_2) \mathbf{i} - (a_1b_3 - a_3b_1) \mathbf{j} + (a_1b_2 - a_2b_1) \mathbf{k}\]
What is a Normal Vector?
A normal vector to a plane provides a lot of information about the plane itself. Essentially, it is a vector that is perpendicular to the plane. For the equation of a plane like \( ax + by + cz + d = 0 \), the coefficients \( a, b, \) and \( c \) form the components of a normal vector.
- For the plane \( 4x - 3y + 2z + 5 = 0 \), the normal vector is \( \mathbf{n_1} = (4, -3, 2) \).
- For the plane \( 3x + 2y - z + 11 = 0 \), the normal vector is \( \mathbf{n_2} = (3, 2, -1) \).
Exploring the Line of Intersection
The line of intersection between two planes can be somewhat of a puzzle. In geometric space, when two distinct planes meet, they typically form a line at that junction — their line of intersection. To describe this line, you often need a direction vector and a point through which the line passes.
- In our problem, this direction vector is derived from the cross product of the normal vectors of the two planes.
- Thus, the vector \((-1, 10, 17)\) describes the direction of the line where these planes intersect.
Understanding Perpendicular Planes
Perpendicular planes are a special geometric construction where two planes meet at a right angle. For a given line, if a plane is perpendicular to it, the normal vector of the plane and the direction vector of the line are the same.
- In this exercise, we begin with a known point \((6, 2, -1)\) and our calculated direction vector from the cross product, \((-1, 10, 17)\).
- These pieces establish the conditions necessary to construct a plane that is perpendicular to the line of intersection of the given planes.