Chapter 12: Problem 17
Find $$\mathbf{a}+\mathbf{b}, 2 \mathbf{a}+3 \mathbf{b},|\mathbf{a}|, \text { and }|\mathbf{a} \mathbf{b}|$$ $$\mathbf{a}=\langle 5,-12\rangle, \quad \mathbf{b}=\langle- 3,-6\rangle$$
Short Answer
Expert verified
\(\mathbf{a} + \mathbf{b} = \langle 2, -18 \rangle\), \(2\mathbf{a} + 3\mathbf{b} = \langle 1, -42 \rangle\), \(|\mathbf{a}| = 13\)."
Step by step solution
01
Adding Vectors \(\mathbf{a} + \mathbf{b}\)
To find \(\mathbf{a} + \mathbf{b}\), add the corresponding components of each vector. Given \(\mathbf{a} = \langle 5, -12 \rangle\) and \(\mathbf{b} = \langle -3, -6 \rangle\), add the x-components and y-components:\[\mathbf{a} + \mathbf{b} = \langle 5 + (-3), -12 + (-6) \rangle = \langle 2, -18 \rangle\]
02
Linear Combination \(2\mathbf{a} + 3\mathbf{b}\)
To find \(2\mathbf{a} + 3\mathbf{b}\), first multiply each vector by their scalar and then add the results. Compute:\[2\mathbf{a} = 2 \times \langle 5, -12 \rangle = \langle 10, -24 \rangle\]\[3\mathbf{b} = 3 \times \langle -3, -6 \rangle = \langle -9, -18 \rangle\]Add these results:\[2\mathbf{a} + 3\mathbf{b} = \langle 10, -24 \rangle + \langle -9, -18 \rangle = \langle 1, -42 \rangle\]
03
Calculate the Magnitude \(|\mathbf{a}|\)
The magnitude of a vector \(\mathbf{a} = \langle x, y \rangle\) is given by \(|\mathbf{a}| = \sqrt{x^2 + y^2}\). For \(\mathbf{a} = \langle 5, -12 \rangle\),\[|\mathbf{a}| = \sqrt{5^2 + (-12)^2} = \sqrt{25 + 144} = \sqrt{169} = 13\]
04
Checking Question on \(|\mathbf{a} \mathbf{b}|\)
There is no standard vector operation denoted as \(|\mathbf{a} \mathbf{b}|\). If it means the magnitude of the dot product of \(\mathbf{a}\) and \(\mathbf{b}\), it should be calculated as \(\mathbf{a} \cdot \mathbf{b}\). The dot product is:\[\mathbf{a} \cdot \mathbf{b} = (5)(-3) + (-12)(-6) = -15 + 72 = 57\]However, since a vector multiplication type isn't specified, we should assume no answer is needed for this section.
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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 vector mathematics that combines two vectors to create a resultant vector. Picture two arrows on a graph representing vectors. Adding them involves shifting one vector so that its tail resides at the head of the other, then drawing a new arrow from the start of the fixed vector to the endpoint of the second.
- To add vectors, sum up their corresponding components. For instance, for vectors \( \mathbf{a} = \langle 5, -12 \rangle \) and \( \mathbf{b} = \langle -3, -6 \rangle \), add \( 5 + (-3) = 2 \) and \( -12 + (-6) = -18 \).
- The resulting vector is \( \langle 2, -18 \rangle \). This new vector illustrates the additive synthesis of \( \mathbf{a} \) and \( \mathbf{b} \).
Scalar Multiplication
Scalar multiplication involves stretching or compressing a vector by a scalar value. Think of changing the length of a string without altering its orientation.
- Each vector component gets multiplied by the scalar: for \( 2 \mathbf{a} \), multiply each part of \( \mathbf{a} = \langle 5, -12 \rangle \) by 2, yielding \( \langle 10, -24 \rangle \).
- Similarly, for \( 3 \mathbf{b} \), with \( \mathbf{b} = \langle -3, -6 \rangle \), scale each component by 3, resulting in \( \langle -9, -18 \rangle \).
Magnitude of a Vector
The magnitude of a vector represents its length, analogous to the hypotenuse in a right triangle.To find the magnitude of vector \( \mathbf{a} = \langle x, y \rangle \), apply the Pythagorean theorem:
- Compute \( |\mathbf{a}| = \sqrt{x^2 + y^2} \).
- For \( \mathbf{a} = \langle 5, -12 \rangle \), this equates to \( \sqrt{5^2 + (-12)^2} = \sqrt{25 + 144} = \sqrt{169} = 13 \).
Dot Product
The dot product of two vectors yields a scalar result and is valuable for finding angles between vectors or determining orthogonality.To calculate the dot product, multiply corresponding vector components and sum them:
- For vectors \( \mathbf{a} = \langle 5, -12 \rangle \) and \( \mathbf{b} = \langle -3, -6 \rangle \), compute \( \mathbf{a} \cdot \mathbf{b} = (5)(-3) + (-12)(-6) = -15 + 72 = 57 \).
- This operation's result, 57, reveals the degree of parallelism or angle between the vectors.