Math Problem Statement

Let T: R^2 → R^2 be the linear transformation that first reflects points through the x-axis and then reflects points through the line y = -x. Find the standard matrix A for T.

Solution

We are tasked with finding the standard matrix AA for the linear transformation TT, which involves two consecutive reflections. The transformation first reflects points through the xx-axis, and then reflects points through the line y=xy = -x.

Step-by-step solution:

  1. Reflection through the xx-axis:

    The matrix for reflecting a point through the xx-axis is: Rx=[1001]R_x = \begin{bmatrix} 1 & 0 \\ 0 & -1 \end{bmatrix} This matrix leaves the xx-coordinate unchanged but negates the yy-coordinate.

  2. Reflection through the line y=xy = -x:

    The matrix for reflecting a point through the line y=xy = -x is: Ry=x=[0110]R_{y=-x} = \begin{bmatrix} 0 & -1 \\ -1 & 0 \end{bmatrix} This swaps the xx- and yy-coordinates and changes their signs.

  3. Composite transformation:

    Since the transformation TT consists of first reflecting through the xx-axis and then through the line y=xy = -x, the standard matrix for TT is the product of these two matrices: A=Ry=xRxA = R_{y=-x} \cdot R_x Let's calculate this:

    A=[0110][1001]A = \begin{bmatrix} 0 & -1 \\ -1 & 0 \end{bmatrix} \cdot \begin{bmatrix} 1 & 0 \\ 0 & -1 \end{bmatrix}

  4. Matrix multiplication: A=[0×1+(1)×00×0+(1)×(1)(1)×1+0×0(1)×0+0×(1)]A = \begin{bmatrix} 0 \times 1 + (-1) \times 0 & 0 \times 0 + (-1) \times (-1) \\ (-1) \times 1 + 0 \times 0 & (-1) \times 0 + 0 \times (-1) \end{bmatrix} Simplifying each element: A=[0110]A = \begin{bmatrix} 0 & 1 \\ -1 & 0 \end{bmatrix}

Thus, the standard matrix AA for the transformation TT is: A=[0110]A = \begin{bmatrix} 0 & 1 \\ -1 & 0 \end{bmatrix}

Would you like any further details or explanations on this problem? Here are five related questions you could explore:

  1. What is the effect of reflecting through the line y=xy = x instead of y=xy = -x?
  2. How do you find the matrix for a general reflection through any line?
  3. Can a reflection be represented by a rotation matrix?
  4. How does matrix multiplication order affect transformations?
  5. How would the transformation change if reflected first through the line y=xy = -x and then through the xx-axis?

Tip: When performing transformations, always pay attention to the order of operations—matrix multiplication is not commutative!

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Math Problem Analysis

Mathematical Concepts

Linear Algebra
Matrix Transformations
Reflections

Formulas

Matrix for reflection through x-axis: R_x = [[1, 0], [0, -1]]
Matrix for reflection through y = -x: R_y=-x = [[0, -1], [-1, 0]]
Composite transformation: A = R_y=-x * R_x

Theorems

Matrix multiplication
Linear transformation

Suitable Grade Level

College (Linear Algebra)