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Find the standard matrix of the given linear transformation from \(\mathbb{R}^{2}\) to \(\mathbb{R}^{2}\). Clockwise rotation through \(30^{\circ}\) about the origin

Short Answer

Expert verified
The standard matrix is \(\begin{bmatrix} \frac{\sqrt{3}}{2} & \frac{1}{2} \\ -\frac{1}{2} & \frac{\sqrt{3}}{2} \end{bmatrix}.\)

Step by step solution

01

Identify Transformation Matrix

For a linear transformation representing clockwise rotation by an angle of \( \theta \) degrees about the origin, the standard matrix is given by: \[A = \begin{bmatrix} \cos \theta & \sin \theta \ -\sin \theta & \cos \theta \end{bmatrix}\]Here, \( \theta = 30^{\circ} \). We will calculate the matrix components based on this angle.
02

Convert Angle to Radians

Since trigonometric functions in transformation matrices use angles in radians, convert \(30^{\circ}\) to radians: \[\theta = 30^{\circ} \times \frac{\pi}{180^{\circ}} = \frac{\pi}{6}\]This is the angle we will use in the matrix components.
03

Calculate Cosine and Sine

Compute the cosine and sine for \( \frac{\pi}{6} \):\[\cos \frac{\pi}{6} = \frac{\sqrt{3}}{2}\]\[\sin \frac{\pi}{6} = \frac{1}{2}\]These values will substitute into the transformation matrix.
04

Construct Transformation Matrix

Substitute \( \cos \frac{\pi}{6} \) and \( \sin \frac{\pi}{6} \) into the transformation matrix: \[A = \begin{bmatrix} \frac{\sqrt{3}}{2} & \frac{1}{2} \ -\frac{1}{2} & \frac{\sqrt{3}}{2} \end{bmatrix}\]This matrix represents the clockwise rotation by \(30^{\circ}\) around the origin.

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Key Concepts

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

Standard Matrix
When we talk about linear transformations, especially in the realm of \( \mathbb{R}^{2} \), the term "standard matrix" is crucial. This matrix effectively represents the transformation in a compact form. For a transformation that involves rotations or reflections, knowing how to construct this matrix is a powerful tool. The standard matrix for any transformation from \( \mathbb{R}^{2} \) to \( \mathbb{R}^{2} \) is a \( 2 \times 2 \) matrix. This matrix allows us to apply the transformation to any vector in \( \mathbb{R}^{2} \) by multiplying them.
For rotations, as in this exercise, the standard matrix utilizes trigonometric functions to represent the rotation angle. The elements of the matrix correspond to the cosine and sine of the rotation angle, appropriately placed to ensure the correct rotational direction is applied while maintaining the vector's magnitude and direction.
  • The first row captures the transformed x-component using: \(\cos \theta \) and \( \sin \theta \)
  • The second row handles the y-component: \(-\sin \theta \) and \(\cos \theta \)
Clockwise Rotation
In transformations, direction matters significantly. A clockwise rotation means turning in the direction that the hands of a clock move. Understanding clockwise rotations ensures correct application, especially in geometric transformations or when combining multiple transformations together.
Rotating an object or coordinate system about the origin modifies its orientation while maintaining its shape and size. Mathematically, representing such a rotation involves using trigonometric functions.
  • Clockwise motion contrasts with counterclockwise, which is often a default assumption in mathematics unless specified otherwise.
  • When dealing with a clockwise rotation by an angle \(\theta\), the standard matrix formula involves changing the sign of the sine components in a rotation matrix.
Understanding these properties helps in constructing the right matrix and subsequently transforming vectors accurately with respect to the desired rotation direction.
Trigonometric Functions
Trigonometric functions like sine and cosine are fundamental in many areas of mathematics and physics, acting as building blocks for transformations. When we talk about rotations, these functions become even more pivotal.
For a given angle, cosine represents the adjacent side over the hypotenuse in a right triangle, and sine represents the opposite side over the hypotenuse. In the context of the rotation matrix, these functions dictate the new components of any transformed vector.
  • The function \( \cos \theta \) helps in maintaining the magnitude of the x-coordinate of vectors during and after transformation.
  • The function \( \sin \theta \) adjusts the influence on the y-coordinate, thus determining the final orientation in space.
  • For clockwise rotations, the sine term inverts, effectively moving the vector in sync with the rotation's directional intention.
Recognizing these roles helps to understand transformations more deeply and cements the understanding of how vectors change their orientation when rotated.
Angle Conversion
In mathematics and physics, angle measurements are essential and often come in two main forms: degrees and radians. For transformations, it's common to convert degrees to radians since radians naturally relate to circles and trigonometric functions.
Radians offer a more natural measurement for mathematical computations because of their direct linkage to a circle's arc length. The conversion is given by the simple formula: \[ \theta = \theta^{\circ} \times \frac{\pi}{180^{\circ}} \]
  • One full rotation (360 degrees) is equal to \(2\pi\) radians.
  • A quarter rotation (90 degrees) is equivalent to \(\frac{\pi}{2}\) radians.
For the exercise in question, the 30-degree angle is converted to radians as \(\frac{\pi}{6}\). Understanding and applying this conversion lets us calculate the trigonometric values precisely, necessary for constructing the correct transformation matrix. Therefore, always remember to convert degrees to radians while dealing with transformations involving trigonometric functions.

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Most popular questions from this chapter

Let \(P=\left[\begin{array}{cc}0.5 & 0.3 \\ 0.5 & 0.7\end{array}\right]\) be the transition matrix for a Markov chain with two states. Let \(\mathbf{x}_{0}=\left[\begin{array}{l}0.5 0.5\end{array}\right]\) be the initial state vector for the population. Compute \(\mathbf{x}_{1}\) and \(\mathbf{x}_{2}\).

A study of piñon (pine) nut crops in the American southwest from 1940 to 1947 hypothesized that nut production followed a Markov chain. [See D. H. Thomas,"A Computer Simulation Model of Great Basin Shoshonean Subsistence and Settlement Patterns," in D. L. Clarke, ed., Models in Archaeology (London: Methuen, \(1972 \text { ). }]\) The data suggested that if one year's crop was good, then the probabilities that the following year's crop would be good, fair, or poor were \(0.08,0.07,\) and \(0.85,\) respectively; if one year's crop was fair, then the probabilities that the following year's crop would be good, fair, or poor were 0.09 \(0.11,\) and \(0.80,\) respectively; if one year's crop was poor, then the probabilities that the following year's crop would be good, fair, or poor were \(0.11,0.05,\) and \(0.84,\) respectively (a) Write down the transition matrix for this Markov chain. (b) If the pinon nut crop was good in \(1940,\) find the probabilities of a good crop in the years 1941 through 1945 (c) In the long run, what proportion of the crops will be good, fair, and poor?

Give a counterexample to show that the given transformation is not a linear transformation. $$T\left[\begin{array}{l} x \\ y \end{array}\right]=\left[\begin{array}{l} y \\ x^{2} \end{array}\right]$$

A graph is called bipartite if its vertices can be subdivided into two sets U and \(V\) such that every edge has one endpoint in U and the other endpoint in \(V\). For example, the graph in Exercise 28 is bipartite with \(U=\left\\{v_{1}, v_{2}, v_{3}\right\\}\) and $V=\left\\{v_{4}, v_{5}\right\\} . Determine whether a graph with the given adjacency matrix is bipartite. $$\left[\begin{array}{cccccc} 0 & 0 & 1 & 0 & 1 & 1 \\ 0 & 0 & 1 & 0 & 1 & 1 \\ 1 & 1 & 0 & 1 & 0 & 0 \\ 0 & 0 & 1 & 0 & 1 & 1 \\ 1 & 1 & 0 & 1 & 0 & 0 \\ 1 & 1 & 0 & 1 & 0 & 0 \end{array}\right]$$

Answer by considering the matrix with the given vectors as its columns. Do \(\left[\begin{array}{l}1 \\ 1 \\ 1 \\\ 0\end{array}\right],\left[\begin{array}{l}1 \\ 1 \\ 0 \\\ 1\end{array}\right],\left[\begin{array}{l}1 \\ 0 \\ 1 \\\ 1\end{array}\right],\left[\begin{array}{l}0 \\ 1 \\ 1 \\\ 1\end{array}\right]\) form a basis for \(\mathbb{R}^{4} ?\)

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