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Find the indicated quantity, assuming \(\mathbf{u}=2 \mathbf{i}+\mathbf{j}, \mathbf{v}=\mathbf{i}-3 \mathbf{j},\) and \(\mathbf{w}=3 \mathbf{i}+4 \mathbf{j}\) $$ (\mathbf{u} \cdot \mathbf{v})(\mathbf{u} \cdot \mathbf{w}) $$

Short Answer

Expert verified
The value of the expression is -10.

Step by step solution

01

Understand Dot Product Formula

The dot product of vectors \( \mathbf{a} = a_1 \mathbf{i} + a_2 \mathbf{j} \) and \( \mathbf{b} = b_1 \mathbf{i} + b_2 \mathbf{j} \) is calculated as \( \mathbf{a} \cdot \mathbf{b} = a_1b_1 + a_2b_2 \). We will use this formula to find the dot products \( \mathbf{u} \cdot \mathbf{v} \) and \( \mathbf{u} \cdot \mathbf{w} \).
02

Calculate \( \mathbf{u} \cdot \mathbf{v} \)

Insert the components of \( \mathbf{u} \) and \( \mathbf{v} \) into the dot product formula. Compute \( (2)(1) + (1)(-3) = 2 - 3 = -1 \). Thus, \( \mathbf{u} \cdot \mathbf{v} = -1 \).
03

Calculate \( \mathbf{u} \cdot \mathbf{w} \)

Insert the components of \( \mathbf{u} \) and \( \mathbf{w} \) into the dot product formula. Compute \( (2)(3) + (1)(4) = 6 + 4 = 10 \). Thus, \( \mathbf{u} \cdot \mathbf{w} = 10 \).
04

Compute the Desired Expression

Compute the product \( (\mathbf{u} \cdot \mathbf{v})(\mathbf{u} \cdot \mathbf{w}) = (-1)(10) = -10 \). This is the desired quantity.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Vector Operations
Vector operations are fundamental to understanding various aspects of mathematics and physics. They allow you to manipulate vectors to obtain meaningful results. Some common vector operations include addition, subtraction, scalar multiplication, and dot product.

Among these, the dot product is particularly useful because it provides a way to quantify how much one vector goes in the direction of another.
  • **Addition**: Combining vectors by adding their corresponding components.
  • **Subtraction**: Finding the difference by subtracting the components of one vector from another.
  • **Scalar Multiplication**: Scaling a vector by multiplying each component by a constant.
  • **Dot Product**: Calculating a single number from two vectors, indicating the degree of their alignment.
For example, with vectors \(\mathbf{u} = 2 \mathbf{i} + \mathbf{j}\) and \(\mathbf{v} = \mathbf{i} - 3 \mathbf{j}\), using the dot product formula, you find the result \(\mathbf{u} \cdot \mathbf{v} = -1\).

It shows a partial alignment in opposite directions, which is crucial in various applications like finding angles between vectors or projections.
Algebra
Algebra is a broad area of mathematics that involves solving equations and understanding how variables interact. It provides the tools needed to manipulate and solve expressions involving vectors.

In the context of vectors, you utilize algebraic principles to compute operations like the dot product. The basic formula for the dot product \(\mathbf{a} \cdot \mathbf{b} = a_1b_1 + a_2b_2\), where \(\mathbf{a} = a_1\mathbf{i} + a_2\mathbf{j}\)and\(\mathbf{b} = b_1\mathbf{i} + b_2\mathbf{j}\).This demonstrates how algebra becomes essential in higher mathematical concepts.

The simplicity of this operation is enhanced by the core algebraic concept of multiplying corresponding terms and summing them, as shown in Step 2 and Step 3 of the solution for \(\mathbf{u} \cdot \mathbf{v}\) and \(\mathbf{u} \cdot \mathbf{w}\).Algebra also provides clarity in ensuring these operations are performed systematically and accurately.
Vectors
Vectors are essential in representing quantities that have both magnitude and direction. In various mathematical and physical contexts, vectors allow for clear and efficient problem-solving. For instance, they can convey information about displacement, velocity, or forces acting on an object.

Each vector can be broken down into components that align with the standard axes. In two dimensions, these components correspond to the \(\mathbf{i}\) and \(\mathbf{j}\) unit vectors. For example:
  • \(\mathbf{u} = 2 \mathbf{i} + \mathbf{j}\): This vector points more along the \(\mathbf{i}\) or x-axis.
  • \(\mathbf{v} = \mathbf{i} - 3 \mathbf{j}\): This vector extends heavily in the opposite direction of the y-axis.
  • \(\mathbf{w} = 3 \mathbf{i} + 4 \mathbf{j}\): Points to both positive x and y directions strongly.
By understanding these components, one can quickly engage with problems involving vectors. The operations performed, such as dot products, hinge on a strong grasp of these component representations. This knowledge is vital to perform operations like the dot product effectively, aiding in detecting relationships like orthogonality or angle finding between vectors.

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Most popular questions from this chapter

Same Line: Different Parametric Equations Every line can be described by infinitely many different sets of parametric equations, since any point on the line and any vector parallel to the line can be used to construct the equations. But how can we tell whether two sets of parametric equations rep- resent the same line? Consider the following two sets of para- metric equations: Line \(1 : \quad x=1-t, \quad y=3 t, \quad z=-6+5 t\) Line \(2 : \quad x=-1+2 t, \quad y=6-6 t, \quad z=4-10 t\) (a) Find two points that lie on Line 1 by setting \(t=0\) and \(t=1\) in its parametric equations. Then show that these points also lie on Line 2 by finding two values of the parameter that give these points when substituted into the parametric equations for Line 2 . (b) Show that the following two lines are not the same by finding a point on Line 3 and then showing that it does not lie on Line \(4 .\) Line \(3 : \quad x=4 t, \quad y=3-6 t, \quad z=-5+2 t\) Line \(4 : \quad x=8-2 t, \quad y=-9+3 t, \quad z=6-t\)

Lines and Planes A line is parallel to the vector \(\mathbf{v},\) and a plane has normal vector \(\mathbf{n}\) . (a) If the line is perpendicular to the plane, what is the relationship between \(\mathbf{v}\) and \(\mathbf{n}\) (parallel or perpendicular)? (b) If the line is parallel to the plane (that is, the line and the plane do not intersect), what is the relationship between \(\mathbf{v}\) and \(\mathbf{n}(\text { parallel or perpendicular) } ?\) (c) Parametric equations for two lines are given. Which line is parallel to the plane \(x-y+4 z=6 ?\) Which line is perpendicular to this plane? Line \(1 : \quad x=2 t, \quad y=3-2 t, \quad z=4+8 t\) Line \(2 : \quad x=-2 t, \quad y=5+2 t, \quad z=3+t\)

(a) Calculate proj, \(\mathbf{u}\) . (b) Resolve \(\mathbf{u}\) into \(\mathbf{u}_{1}\) and \(\mathbf{u}_{2},\) where \(\mathbf{u}_{1}\) is parallel to \(\mathbf{v}\) and \(\mathbf{u}_{2}\) is orthogonal to \(\mathbf{v} .\) $$ \mathbf{u}=\langle 1,2\rangle, \quad \mathbf{v}=\langle 1,-3\rangle $$

Two vectors \(\mathbf{u}\) and \(\mathbf{v}\) are given. Find their dot product \(\mathbf{u} \cdot \mathbf{v} .\) $$ \mathbf{u}=6 \mathbf{i}-4 \mathbf{j}-2 \mathbf{k}, \quad \mathbf{v}=\frac{5}{6} \mathbf{i}+\frac{3}{2} \mathbf{j}-\mathbf{k} $$

The plane containing the point \(P\left(x_{0}, y_{0}, z_{0}\right)\) and having the normal vector \(\mathbf{n}=\langle a, b, c\rangle\) is described algebraically by the equation ______

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