In Exercises 45–50, determine whether v and w are parallel, orthogonal, or neither. v = 3i - 5j, w = 6i + 18 j 5
Table of contents
- 0. Review of College Algebra4h 45m
- 1. Measuring Angles40m
- 2. Trigonometric Functions on Right Triangles2h 5m
- 3. Unit Circle1h 19m
- 4. Graphing Trigonometric Functions1h 19m
- 5. Inverse Trigonometric Functions and Basic Trigonometric Equations1h 41m
- 6. Trigonometric Identities and More Equations2h 34m
- 7. Non-Right Triangles1h 38m
- 8. Vectors2h 25m
- 9. Polar Equations2h 5m
- 10. Parametric Equations1h 6m
- 11. Graphing Complex Numbers1h 7m
8. Vectors
Dot Product
Problem 43
Textbook Question
In Exercises 43–44, find the angle, in degrees, between v and w.
v = 2 cos(4π/3) i + 2 sin(4π/3) j, w = 3 cos(3π/2) i + 3 sin(3π/2) j
Verified step by step guidance1
Identify the vectors \( \mathbf{v} = 2 \cos(4\pi) \mathbf{i} + 2 \sin(4\pi) \mathbf{j} \) and \( \mathbf{w} = 3 \cos(3\pi) \mathbf{i} + 3 \sin(3\pi) \mathbf{j} \). These are given in component form using trigonometric functions.
Recall that the angle \( \theta \) between two vectors \( \mathbf{v} \) and \( \mathbf{w} \) can be found using the dot product formula:
\[ \mathbf{v} \cdot \mathbf{w} = \|\mathbf{v}\| \|\mathbf{w}\| \cos(\theta) \]
which rearranges to
\[ \theta = \cos^{-1} \left( \frac{\mathbf{v} \cdot \mathbf{w}}{\|\mathbf{v}\| \|\mathbf{w}\|} \right) \].
Calculate the components of \( \mathbf{v} \) and \( \mathbf{w} \) by evaluating the cosine and sine values at the given angles:
- \( \cos(4\pi) \) and \( \sin(4\pi) \)
- \( \cos(3\pi) \) and \( \sin(3\pi) \).
Compute the dot product \( \mathbf{v} \cdot \mathbf{w} \) using the formula:
\[ \mathbf{v} \cdot \mathbf{w} = v_x w_x + v_y w_y \]
where \( v_x, v_y \) and \( w_x, w_y \) are the components of \( \mathbf{v} \) and \( \mathbf{w} \) respectively.
Find the magnitudes \( \|\mathbf{v}\| \) and \( \|\mathbf{w}\| \) using:
\[ \|\mathbf{v}\| = \sqrt{v_x^2 + v_y^2} \quad \text{and} \quad \|\mathbf{w}\| = \sqrt{w_x^2 + w_y^2} \]
Finally, substitute these values into the formula for \( \theta \) and solve for the angle in degrees.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Vector Representation in the Plane
Vectors in the plane can be expressed using their components along the i (x-axis) and j (y-axis) unit vectors. Here, each vector is given in terms of cosine and sine functions, which correspond to the x and y components based on an angle from the positive x-axis. Understanding this allows you to interpret the vectors geometrically and perform calculations.
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Introduction to Vectors
Dot Product and Angle Between Vectors
The dot product of two vectors relates their magnitudes and the cosine of the angle between them: v · w = |v||w|cos(θ). By computing the dot product and magnitudes, you can solve for the angle θ between vectors. This is essential for finding the angle in degrees between v and w.
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Find the Angle Between Vectors
Trigonometric Functions and Angle Measures
Cosine and sine functions describe the coordinates of points on the unit circle at given angles, often in radians. Converting these angles and understanding their periodicity helps simplify vector components and calculate exact values. Recognizing angles like 3π and 4π radians is key to evaluating the vector components correctly.
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Introduction to Trigonometric Functions
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