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Let \(\mathbf{u}=\left\langle u_{1}, u_{2}, u_{3}\right\rangle\) \(\mathbf{v}=\left\langle v_{1}, v_{2}, v_{3}\right\rangle\), and \(\mathbf{w}=\) \(\left\langle w_{1}, w_{2}, w_{3}\right\rangle\). Let \(c\) be a scalar. Prove the following vector properties. \(\mathbf{u} \cdot(\mathbf{v}+\mathbf{w})=\mathbf{u} \cdot \mathbf{v}+\mathbf{u} \cdot \mathbf{w}\)

Short Answer

Expert verified
Question: Prove that the dot product is distributive over vector addition, i.e., \(\mathbf{u}\cdot(\mathbf{v}+\mathbf{w}) = \mathbf{u}\cdot\mathbf{v} + \mathbf{u}\cdot\mathbf{w}\).

Step by step solution

01

Write the vector components

The given vectors \(\mathbf{u}=\left\langle u_{1}, u_{2}, u_{3}\right\rangle\), \(\mathbf{v}=\left\langle v_{1}, v_{2}, v_{3}\right\rangle\), and \(\mathbf{w}=\left\langle w_{1}, w_{2}, w_{3}\right\rangle\).
02

Compute the sum of vectors \(\mathbf{v}\) and \(\mathbf{w}\)

Adding the vectors \(\mathbf{v}\) and \(\mathbf{w}\) component-wise, we get: \(\mathbf{v}+\mathbf{w}=\left\langle v_{1}+w_{1}, v_{2}+w_{2}, v_{3}+w_{3}\right\rangle\).
03

Compute the dot product of \(\mathbf{u}\) with the sum of \(\mathbf{v}\) and \(\mathbf{w}\)

The dot product of \(\mathbf{u}\) with the sum of \(\mathbf{v}\) and \(\mathbf{w}\) is given by: \(\mathbf{u}\cdot(\mathbf{v}+\mathbf{w}) = u_{1}(v_{1}+w_{1}) + u_{2}(v_{2}+w_{2}) + u_{3}(v_{3}+w_{3})\).
04

Distribute the components of \(\mathbf{u}\) in the expression

Distributing the components of \(\mathbf{u}\) in the expression, we get: \(u_{1}v_{1} + u_{1}w_{1} + u_{2}v_{2} + u_{2}w_{2} + u_{3}v_{3} + u_{3}w_{3}\).
05

Group the same type of dot products

Grouping the same type of dot products, we get: \((u_{1}v_{1} + u_{2}v_{2} + u_{3}v_{3}) + (u_{1}w_{1} + u_{2}w_{2} + u_{3}w_{3})\).
06

Recognize the dot product expressions

We can recognize the expressions inside the parentheses as the dot products \(\mathbf{u}\cdot\mathbf{v}\) and \(\mathbf{u}\cdot\mathbf{w}\) respectively. Therefore, we have: \(\mathbf{u}\cdot(\mathbf{v}+\mathbf{w}) = \mathbf{u}\cdot\mathbf{v} + \mathbf{u}\cdot\mathbf{w}\), which completes the proof.

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Key Concepts

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

Dot Product
The dot product is a fundamental operation in vector algebra involving two vectors. It's also known as the scalar product because the result is a scalar value, not a vector. To compute the dot product for any two vectors \(\mathbf{u} = \langle u_1, u_2, u_3 \rangle\) and \(\mathbf{v} = \langle v_1, v_2, v_3 \rangle\), you multiply the corresponding components and sum the results:
  • \(\mathbf{u} \cdot \mathbf{v} = u_1v_1 + u_2v_2 + u_3v_3\)
This operation is critical in various fields such as physics and engineering because it provides a way to compute projections and work done. Additionally, the dot product has geometric interpretations:
  • It measures the angle between two vectors.
  • If the dot product is zero, the vectors are orthogonal (perpendicular to each other).
Understanding the dot product helps in analyzing vector quantities efficiently and forms the basis for more advanced vector operations.
Distributive Property
The distributive property in vector algebra extends a familiar property from arithmetic into the realm of vectors. For vectors, this property highlights how a dot product interacts with vector addition. Specifically, it tells us how the dot product of a vector with a sum of vectors distributes over the addition:
  • \(\mathbf{u} \cdot (\mathbf{v} + \mathbf{w}) = \mathbf{u} \cdot \mathbf{v} + \mathbf{u} \cdot \mathbf{w}\)
This is crucial because it simplifies complex vector expressions and allows for systematic solutions in vector calculus. In our original exercise, by distributing \(\mathbf{u}\) over \(\mathbf{v} + \mathbf{w}\), each term of \(\mathbf{u}\) was multiplied with the corresponding terms in \(\mathbf{v}\) and \(\mathbf{w}\) individually.
The property is beneficial in computational fields as it aids in optimizing performance by reducing the computational load in vector operations. Grasping this concept is key to tackling problems in physics, especially when dealing with forces and vector fields.
Vector Addition
Vector addition is a cornerstone operation in math and physics, necessary for many applications like calculating forces or motion. When adding two vectors, each component is added separately. Consider vectors \(\mathbf{v} = \langle v_1, v_2, v_3 \rangle\) and \(\mathbf{w} = \langle w_1, w_2, w_3 \rangle\):
  • The resultant vector is \(\mathbf{v} + \mathbf{w} = \langle v_1 + w_1, v_2 + w_2, v_3 + w_3 \rangle\)
Graphically, vector addition is often referred to as the 'tip-to-tail' method, where the tail of one vector is placed at the tip of another, producing a new vector that spans from the start of the first to the end of the second.
This method lays the groundwork for exploring vector spaces and ensuring that the combination of any two vectors yields another vector within the same space. Understanding vector addition is essential, as it allows us to build and break down vector systems efficiently, a skill applicable in diverse fields like engineering and programming.

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Most popular questions from this chapter

An object moves along a path given by \(\mathbf{r}(t)=\langle a \cos t+b \sin t, c \cos t+d \sin t\rangle, \quad\) for \(0 \leq t \leq 2 \pi\) a. What conditions on \(a, b, c,\) and \(d\) guarantee that the path is a circle? b. What conditions on \(a, b, c,\) and \(d\) guarantee that the path is an ellipse?

Imagine three unit spheres (radius equal to 1 ) with centers at \(O(0,0,0), P(\sqrt{3},-1,0)\) and \(Q(\sqrt{3}, 1,0) .\) Now place another unit sphere symmetrically on top of these spheres with its center at \(R\) (see figure). a. Find the coordinates of \(R\). (Hint: The distance between the centers of any two spheres is 2.) b. Let \(\mathbf{r}_{i j}\) be the vector from the center of sphere \(i\) to the center of sphere \(j .\) Find \(\mathbf{r}_{O P}, \mathbf{r}_{O Q}, \mathbf{r}_{P Q}, \mathbf{r}_{O R},\) and \(\mathbf{r}_{P R}\).

Find the domains of the following vector-valued functions. $$\mathbf{r}(t)=\sqrt{4-t^{2}} \mathbf{i}+\sqrt{t} \mathbf{j}-\frac{2}{\sqrt{1+t}} \mathbf{k}$$

A baseball leaves the hand of a pitcher 6 vertical feet above home plate and \(60 \mathrm{ft}\) from home plate. Assume that the coordinate axes are oriented as shown in the figure. a. In the absence of all forces except gravity, assume that a pitch is thrown with an initial velocity of \(\langle 130,0,-3\rangle \mathrm{ft} / \mathrm{s}\) (about \(90 \mathrm{mi} / \mathrm{hr}\) ). How far above the ground is the ball when it crosses home plate and how long does it take for the pitch to arrive? b. What vertical velocity component should the pitcher use so that the pitch crosses home plate exactly \(3 \mathrm{ft}\) above the ground? c. A simple model to describe the curve of a baseball assumes that the spin of the ball produces a constant sideways acceleration (in the \(y\) -direction) of \(c \mathrm{ft} / \mathrm{s}^{2}\). Assume a pitcher throws a curve ball with \(c=8 \mathrm{ft} / \mathrm{s}^{2}\) (one-fourth the acceleration of gravity). How far does the ball move in the \(y\) -direction by the time it reaches home plate, assuming an initial velocity of (130,0,-3) ft/s? d. In part (c), does the ball curve more in the first half of its trip to the plate or in the second half? How does this fact affect the batter? e. Suppose the pitcher releases the ball from an initial position of (0,-3,6) with initial velocity \((130,0,-3) .\) What value of the spin parameter \(c\) is needed to put the ball over home plate passing through the point (60,0,3)\(?\)

Suppose \(\mathbf{u}\) and \(\mathbf{v}\) are nonzero vectors in \(\mathbb{R}^{3}\). a. Prove that the equation \(\mathbf{u} \times \mathbf{z}=\mathbf{v}\) has a nonzero solution \(\mathbf{z}\) if and only if \(\mathbf{u} \cdot \mathbf{v}=0 .\) (Hint: Take the dot product of both sides with v.) b. Explain this result geometrically.

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