Chapter 5: Problem 59
In Problems \(49-62, \mathbf{u}=\langle 2,-3\rangle, \mathbf{v}=\langle-1,5\rangle,\) and \(\mathbf{w}=\langle 3,-2\rangle .\) Find the indicated scalar or vector. $$ \mathbf{u} \cdot(\mathbf{u}+\mathbf{v}+\mathbf{w}) $$
Short Answer
Expert verified
The scalar product is 8.
Step by step solution
01
Understand the Dot Product
The dot product between two vectors \( \mathbf{a} = \langle a_1, a_2 \rangle \) and \( \mathbf{b} = \langle b_1, b_2 \rangle \) is calculated using the formula \( \mathbf{a} \cdot \mathbf{b} = a_1b_1 + a_2b_2 \). This will be used to find \( \mathbf{u} \cdot (\mathbf{u} + \mathbf{v} + \mathbf{w}) \).
02
Find the Result of the Vector Addition
Compute the sum of the vectors \( \mathbf{u}, \mathbf{v}, \text{ and } \mathbf{w} \). First, add their components individually: \( \mathbf{u} + \mathbf{v} + \mathbf{w} = \langle 2, -3 \rangle + \langle -1, 5 \rangle + \langle 3, -2 \rangle \). Start by adding \( \langle 2 + (-1), -3 + 5 \rangle = \langle 1, 2 \rangle \). Then add \( \langle 1, 2 \rangle \) and \( \langle 3, -2 \rangle \) to obtain \( \langle 1+3, 2-2 \rangle = \langle 4, 0 \rangle \).
03
Compute the Dot Product
Now compute \( \mathbf{u} \cdot (\mathbf{u} + \mathbf{v} + \mathbf{w}) \) using \( \mathbf{u} = \langle 2, -3 \rangle \) and the resulting vector from step 2, \( \langle 4, 0 \rangle \). The dot product is \( 2 \times 4 + (-3) \times 0 = 8 + 0 = 8 \).
04
Write the Final Answer
The result of the dot product is \( 8 \). Hence, \( \mathbf{u} \cdot (\mathbf{u} + \mathbf{v} + \mathbf{w}) = 8 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Vector Addition
Vector addition is a fundamental operation in mathematics used to combine two or more vectors into a single vector. Imagine vegetables being tossed into a salad bowl; adding vectors works quite similarly.When you add vectors, you simply sum their corresponding components. For example, if you have vectors \( \mathbf{a} = \langle a_1, a_2 \rangle \) and \( \mathbf{b} = \langle b_1, b_2 \rangle \), their sum is another vector, \( \mathbf{c} = \langle a_1 + b_1, a_2 + b_2 \rangle \).In our exercise, the task was to add \( \mathbf{u} = \langle 2, -3 \rangle \), \( \mathbf{v} = \langle -1, 5 \rangle \), and \( \mathbf{w} = \langle 3, -2 \rangle \). First, add \( \mathbf{u} \) and \( \mathbf{v} \) to get the intermediate result \( \langle 1, 2 \rangle \). Next, add this result to \( \mathbf{w} \), arriving at the final combined vector \( \langle 4, 0 \rangle \).
Properties of Vector Addition
- Commutative property: \( \mathbf{a} + \mathbf{b} = \mathbf{b} + \mathbf{a} \)
- Associative property: \( (\mathbf{a} + \mathbf{b}) + \mathbf{c} = \mathbf{a} + (\mathbf{b} + \mathbf{c}) \)
- Adding the zero vector does not change a vector: \( \mathbf{a} + \mathbf{0} = \mathbf{a} \)
Vector Components
Vector components are simply the individual elements or parts of a vector. Picture a vector as an arrow pointing from one location to another. The components tell you exactly how far and in what direction you move along each axis.For a 2-dimensional vector \( \mathbf{v} = \langle v_1, v_2 \rangle \), \( v_1 \) and \( v_2 \) represent the distance along the horizontal (x-axis) and vertical (y-axis) directions, respectively.
Understanding the Role of Components
The components are crucial for various vector operations:- They allow you to easily compute the vector's magnitude (or length) using the formula \( \sqrt{v_1^2 + v_2^2} \).
- They make adding vectors straightforward, as each component can simply be added to its counterpart from another vector.
- The components are used in calculating dot products and determining angles between vectors.
Scalar Multiplication
Scalar multiplication involves multiplying each component of a vector by a scalar (a real number). It's like scaling a toy; if you double the size, all parts grow twice as large!If you have a vector \( \mathbf{v} = \langle v_1, v_2 \rangle \) and a scalar \( c \), then after scalar multiplication, you get a new vector \( \mathbf{c} = \langle c \cdot v_1, c \cdot v_2 \rangle \).
Impacts of Scalar Multiplication
- Alters the vector's magnitude, making it larger or smaller depending on the scalar's value.
- May change the vector's direction if the scalar is negative, flipping it around its origin.
- Retains the vector’s direction if the scalar is positive.