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One of the properties of the dot product is that \((\mathbf{u}+\mathbf{v}) \cdot \mathbf{w}=(\mathbf{u} \cdot \mathbf{w})+(\mathbf{v} \cdot \mathbf{w})\) That is, the dot product distributes over vector addition on the right. Here we investigate whether the dot product distributes over vector addition on the left. a. Let \(\mathbf{u}=\langle 1,2,-1\rangle, \mathbf{v}=\langle 4,-3,6\rangle,\) and \(\mathbf{v}=\langle 4,7,2\rangle .\) Calculate $$ \mathbf{u} \cdot(\mathbf{v}+\mathbf{w}) \text { and }(\mathbf{u} \cdot \mathbf{v})+(\mathbf{u} \cdot \mathbf{w}) $$ What do you notice? b. Use the properties of the dot product to show that in general $$ \mathbf{x} \cdot(\mathbf{y}+\mathbf{z})=(\mathbf{x} \cdot \mathbf{y})+(\mathbf{x} \cdot \mathbf{z}) $$ for any vectors \(\mathbf{x}, \mathbf{y},\) and \(\mathbf{z}\) in \(\mathbb{R}^{n}\).

Short Answer

Expert verified
For any vectors \(\mathbf{x}\), \(\mathbf{y}\), and \(\mathbf{z}\), \(\mathbf{x} \cdot(\mathbf{y}+\mathbf{z})=(\mathbf{x} \cdot \mathbf{y})+(\mathbf{x} \cdot \mathbf{z})\), which shows that the dot product indeed distributes over vector addition on the left side as well. This is derived through a series of steps, including calculating the dot product of 饾惐 and (饾惒+饾惓), distributing the 饾惐 components, rearranging the summation terms, and rewriting the summations as dot products.

Step by step solution

01

Add the vectors 饾惎 and 饾惏

Add the vectors 饾惎 and 饾惏: \(\mathbf{v}+\mathbf{w}=\langle 4,-3,6 \rangle + \langle 4,7,2 \rangle = \langle 8,4,8 \rangle\)
02

Calculate the dot product of 饾惍 and (饾惎+饾惏)

Calculate the dot product of 饾惍 and (饾惎+饾惏): \(\mathbf{u} \cdot (\mathbf{v}+\mathbf{w}) = \langle 1,2,-1 \rangle \cdot \langle 8,4,8 \rangle = (1 \times 8) + (2 \times 4) + (-1 \times 8) = 8 + 8 - 8 = 8\)
03

Calculate the individual dot products of 饾惍 and 饾惎, and 饾惍 and 饾惏

Calculate the individual dot products: \(\mathbf{u} \cdot \mathbf{v} = \langle 1,2,-1 \rangle \cdot \langle 4,-3,6 \rangle = (1 \times 4) + (2 \times -3) + (-1 \times 6) = 4 - 6 - 6 = -8\) \(\mathbf{u} \cdot \mathbf{w} = \langle 1,2,-1 \rangle \cdot \langle 4,7,2 \rangle = (1 \times 4) + (2 \times 7) + (-1 \times 2) = 4 + 14 - 2 = 16\)
04

Sum the individual dot products

Add the individual dot products: \((\mathbf{u} \cdot \mathbf{v})+(\mathbf{u} \cdot \mathbf{w}) = (-8) + 16 = 8\) Note that the results from Steps 2 and 4 are the same: both are equal to 8. This suggests the distributive property holds for the dot product on the left side as well. **Task B** Let \(\mathbf{x} = \langle x_1, x_2, \ldots, x_n \rangle\), \(\mathbf{y} = \langle y_1, y_2, \ldots, y_n \rangle\), and \(\mathbf{z} = \langle z_1, z_2, \ldots, z_n \rangle\).
05

Calculate the dot product of 饾惐 and (饾惒+饾惓)

Calculate the dot product of 饾惐 and (饾惒+饾惓): \(\mathbf{x} \cdot (\mathbf{y}+\mathbf{z}) = \langle x_1, x_2, \ldots, x_n \rangle \cdot \langle y_1+z_1, y_2+z_2, \ldots, y_n+z_n \rangle = \sum_{i=1}^n x_i(y_i+z_i)\)
06

Distribute the 饾惐 components

Distribute the 饾惐 components over the corresponding components in the sum: \(\sum_{i=1}^n x_i(y_i+z_i) = \sum_{i=1}^n (x_i y_i + x_i z_i)\)
07

Rearrange the summation terms

Rearrange the summation terms to separate the individual dot products: \(\sum_{i=1}^n (x_i y_i + x_i z_i) = \sum_{i=1}^n x_i y_i + \sum_{i=1}^n x_i z_i\)
08

Rewrite the summations as dot products

Rewrite the summations as dot products: \(\sum_{i=1}^n x_i y_i + \sum_{i=1}^n x_i z_i = (\mathbf{x} \cdot \mathbf{y}) + (\mathbf{x} \cdot \mathbf{z})\) Thus, we have shown that for any vectors \(\mathbf{x}\), \(\mathbf{y}\), and \(\mathbf{z}\), \(\mathbf{x} \cdot(\mathbf{y}+\mathbf{z})=(\mathbf{x} \cdot \mathbf{y})+(\mathbf{x} \cdot \mathbf{z})\), proving the distributive property holds for the dot product on the left side as well.

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Key Concepts

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

Vector Addition
Understanding vector addition is crucial as it forms the base for many operations involving vectors, including the dot product. In simple terms, adding two or more vectors together means summing their corresponding components. For instance, if you have two vectors \( \mathbf{a} = \langle a_1, a_2, a_3 \rangle \) and \( \mathbf{b} = \langle b_1, b_2, b_3 \rangle \), their sum \( \mathbf{a} + \mathbf{b} \) is computed as \( \langle a_1+b_1, a_2+b_2, a_3+b_3 \rangle \).
This operation extends naturally to vectors in higher dimensions, such as \( n \)-dimensional space. When performing vector addition, each component is treated independently, making the operation straightforward and intuitive.
The resulting vector from adding two vectors represents a new magnitude and direction, effectively combining the effects of the original vectors. In graphical terms, this can be visualized as placing the tail of one vector at the head of the other, resulting in a diagonal when completed to a parallelogram.
Distributive Property
The distributive property in the context of vectors and dot products is analogous to distribution in algebra. Specifically, when dealing with dot products, this property allows a vector to be distributed across a sum, yielding the same result as the sum of individual dot products. Mathematically, this is illustrated with \( \mathbf{x} \cdot (\mathbf{y} + \mathbf{z}) = (\mathbf{x} \cdot \mathbf{y}) + (\mathbf{x} \cdot \mathbf{z}) \).
This means you can compute a dot product over a sum by separately computing dot products and then adding them together. This property is a crucial simplifier in vector calculus, making computations easier by breaking them into smaller pieces.
It's important to note that this property works whether the distribution is from the right or the left, as seen in the original exercise, where both \( (\mathbf{u}+\mathbf{v}) \cdot \mathbf{w} \) and \( \mathbf{u} \cdot (\mathbf{v}+\mathbf{w}) \) return the same result, ensuring consistency in multivariable calculus.
Multivariable Calculus
Multivariable calculus extends the principles of single-variable calculus into higher dimensions. Vectors play a significant role in this area as they allow for the manipulation and analysis of multi-dimensional data. In addition to handling vectors, multivariable calculus explores functions with multiple inputs and outputs.
Such analysis often involves computing with vectors, where operations like the dot product become essential. The dot product, being an operation that produces a scalar from two vectors, is heavily used in determining angles, projections, and lengths in multi-dimensional space. This is vital when dealing with gradient vectors, divergence, and curl, all of which require a solid understanding of vector operations.
Moreover, the dot product's distributive property fits seamlessly into multivariable calculus. It simplifies the calculus of vector functions, makes it easier to handle linear transformations, and aids in the application of theorems like Green's and Stokes'. Understanding these connections can help students appreciate the power and utility of calculus in analyzing complex, real-world systems.

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Most popular questions from this chapter

Consider the function \(h\) defined by \(h(x, y)=8-\sqrt{4-x^{2}-y^{2}}\). a. What is the domain of \(h ?\) (Hint: describe a set of ordered pairs in the plane by explaining their relationship relative to a key circle.) b. The range of a function is the set of all outputs the function generates. Given that the range of the square root function \(g(t)=\sqrt{t}\) is the set of all nonnegative real numbers, what do you think is the range of \(h ?\) Why? c. Choose 4 different values from the range of \(h\) and plot the corresponding level curves in the plane. What is the shape of a typical level curve? d. Choose 5 different values of \(x\) (including at least one negative value and zero), and sketch the corresponding traces of the function \(h\). e. Choose 5 different values of \(y\) (including at least one negative value and zero), and sketch the corresponding traces of the function \(h\). f. Sketch an overall picture of the surface generated by \(h\) and write at least one sentence to describe how the surface appears visually. Does the surface remind you of a familiar physical structure in nature?

You are looking down at a map. A vector \(\mathbf{u}\) with \(|\mathbf{u}|=7\) points north and a vector \(\mathbf{v}\) with \(|\mathbf{v}|=6\) points northeast. The crossproduct \(\mathbf{u} \times \mathbf{v}\) points: A) south B) northwest C) up D) down Please enter the letter of the correct answer: _______ The magnitude \(|\mathbf{u} \times \mathbf{v}|=\) _________

Recall that given any vector \(\mathbf{v}\), we can calculate its length, \(|\mathbf{v}| .\) Also, we say that two vectors that are scalar multiples of one another are parallel. a. Let \(\mathbf{v}=\langle 3,4\rangle\) in \(\mathbb{R}^{2}\). Compute \(|\mathbf{v}|\), and determine the components of the vector \(\mathbf{u}=\frac{1}{|\mathbf{v}|} \mathbf{v}\). What is the magnitude of the vector \(\mathbf{u}\) ? How does its direction compare to \(\mathbf{v} ?\) b. Let \(\mathbf{w}=3 \mathbf{i}-3 \mathbf{j}\) in \(\mathbb{R}^{2}\). Determine a unit vector \(\mathbf{u}\) in the same direction as \(\mathbf{w}\). c. Let \(\mathbf{v}=\langle 2,3,5\rangle\) in \(\mathbb{R}^{3}\). Compute \(|\mathbf{v}|\), and determine the components of the vector \(\mathbf{u}=\frac{1}{|\mathbf{v}|} \mathbf{v}\). What is the magnitude of the vector \(\mathbf{u}\) ? How does its direction compare to \(\mathbf{v}\) ? d. Let \(\mathbf{v}\) be an arbitrary nonzero vector in \(\mathbb{R}^{3}\). Write a general formula for a unit vector that is parallel to \(\mathbf{v}\).

Find the point at which the line \(\langle 4,2,4\rangle+t\langle-3,-3,-4\rangle\) intersects the plane \(-5 x+5 y-3 z=2\). _________,_________

Consider the two-variable function \(z=f(x, y)=3 x^{2}+4 y^{2}-2\). a. Determine a vector-valued function \(\mathbf{r}\) that parameterizes the curve which is the \(x=2\) trace of \(z=f(x, y) .\) Plot the resulting curve. Do likewise for \(x=-2,-1,0,\) and \(1 .\) b. Determine a vector-valued function \(\mathbf{r}\) that parameterizes the curve which is the \(y=2\) trace of \(z=f(x, y) .\) Plot the resulting curve. Do likewise for \(y=-2,-1,0,\) and \(1 .\) c. Determine a vector-valued function \(\mathbf{r}\) that parameterizes the curve which is the \(z=2\) contour of \(z=f(x, y) .\) Plot the resulting curve. Do likewise for \(z=-2,-1,0,\) and \(1 .\) d. Use the traces and contours you've just investigated to create a wireframe plot of the surface generated by \(z=f(x, y) .\) In addition, write two sentences to describe the characteristics of the surface.

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