Chapter 22: Problem 1
The equation of the plane through the points \((2,3,1)\) and \((4,-5,3)\) and parallel to \(x\)-axis is (A) \(x-z-1=0\) (B) \(4 x+y-11=0\) (C) \(y+4 z-7=0\) (D) none of these
Short Answer
Expert verified
The correct answer is (C) \(y+4z-7=0\).
Step by step solution
01
Determine the direction vector
To find the equation of the plane, we first need a normal vector to the plane. Since the plane is parallel to the x-axis, the direction vector along the x-axis is given by \( \mathbf{d} = (1,0,0) \). We can determine the direction vector from the points \( (2,3,1) \) and \( (4,-5,3) \) as \( \mathbf{v} = (4-2, -5-3, 3-1) = (2, -8, 2) \).
02
Determine another vector parallel to the plane
The plane must have another vector parallel to it, that is orthogonal to the x-axis. We found this vector \( \mathbf{v} = (2, -8, 2) \).
03
Find the normal vector to the plane
The normal vector to the plane \( \mathbf{n} \) is found using the cross product of the direction vectors \( \mathbf{d} = (1,0,0) \) and \( \mathbf{v} = (2, -8, 2) \). The cross product is \[ \mathbf{n} = \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \ 1 & 0 & 0 \ 2 & -8 & 2 \end{vmatrix} = (0, -2, -8) \].
04
Write the equation of the plane
The equation of the plane can be written using the point-normal form as \( \mathbf{n} \cdot (\mathbf{r} - \mathbf{r_0}) = 0 \), where \( \mathbf{r_0} \) is any point on the plane, for example, \( (2,3,1) \), and \( \mathbf{n} = (0, -2, -8) \). Substituting, we have \( 0(x - 2) - 2(y - 3) - 8(z - 1) = 0 \).
05
Simplify the equation
Simplify the equation from Step 4: \( -2(y - 3) - 8(z - 1) = 0 \). Expanding gives \( -2y + 6 - 8z + 8 = 0 \). Simplifying further, we get \( -2y - 8z + 14 = 0 \), which can be rewritten as \( 2y + 8z = 14 \). Dividing through by 2 gives \( y + 4z = 7 \).
06
Match the simplified equation to the given options
The simplified equation \( y + 4z = 7 \) matches option (C) in the given question. Thus, the right choice is option (C).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Direction Vector
A direction vector is a vector that indicates the direction of a line or a vector. It is particularly helpful when finding the equation of a plane. In the context of the exercise, the direction vector can be determined by the difference in coordinates of two points on a line. We used the points \((2,3,1)\) and \((4,-5,3)\) to find the direction vector \(\mathbf{v} = (4-2, -5-3, 3-1)\). This simplifies to \(\mathbf{v} = (2, -8, 2)\).
- The x-component is \(4-2=2\).
- The y-component is \(-5-3=-8\).
- The z-component is \(3-1=2\).
Normal Vector
The normal vector is a perpendicular vector to a plane, critical in defining the plane equation. In our problem, the normal vector \(\mathbf{n}\) is derived through the cross product of two vectors that lie on the plane.
- A normal vector is essential for uniquely defining a plane's position and orientation.
- For the plane parallel to the x-axis, we started with the direction vector \(\mathbf{d} = (1,0,0)\).
Cross Product
The cross product is an operation used to find a vector that is perpendicular to two given vectors, often applied in physics and engineering. In this exercise, it's used to find the normal vector. With vectors \(\mathbf{d} = (1,0,0)\) and \(\mathbf{v} = (2,-8,2)\), their cross product is \[ \mathbf{n} = \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \ 1 & 0 & 0 \ 2 & -8 & 2 \end{vmatrix} = (0, -2, -8) \].
- The result is perpendicular to both input vectors.
- The cross product helps derive the normal vector which is crucial for planes.
Point-Normal Form
The point-normal form is a method to express the equation of a plane, using a point on the plane and the normal vector. It is given by the formula \( \mathbf{n} \cdot (\mathbf{r} - \mathbf{r_0}) = 0 \), where \(\mathbf{r_0}\) is a point on the plane and \(\mathbf{n}\) is the normal vector.
- We use it to transform geometric information into a plane equation.
- It ensures that the plane is accurately depicted through its orientation in 3D space.