Finding a Matrix for Successive Transformations

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Of course, to find the matrix, you need the numerical values of a, b, c and d.In summary, the question is asking for a single matrix that performs the operations of expanding by a factor of 5 in the y-direction and shearing with a factor of 2 in the y-direction. To solve this, we can set up a system of equations using the given transformations and solve for the numerical values of the matrix's coefficients.
  • #1
sara_87
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Homework Statement



find a single matrix that performs the indicated successions of operations:
expands by a factor of 5 in the y-direction, then shears with factor 2
in the y-direction

Homework Equations





The Attempt at a Solution



first for the expansion:
(x,y) maps to (x,5y)
then for the shear:
(x,5y) maps to (x, (2x+5y)

i think its right but I am not quite sure.
thank you.
 
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  • #2
You have written down the transformations correctly but you haven't answered the question! You were asked to find a matrix. What matrix does that?

What matrix changes (x,y) to (x, 2x+ 5y)? In other words, find the a, b, c,d such that
[tex]\left[\begin{array}{cc} a & b \\ c & d\end{array}\right]\left[\begin{array}{c} x \\ y\end{array}\right]= \left[\begin{array}{c} x \\ 2x+ 5y\end{array}\right][/tex]
Multiplying the left side will give you two equations for a, b, c, d but remember they must be true for all x and y. Comparing corresponding coefficients will give you four very simple equations for the a, b, c, d.
 
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  • #3
ok so multipying the left side gives the matrix:
[(ax+by),(cx+dy)]
so ax+by=x
cx+dy=2x+5y

now what? ;)
 
  • #4
You might separate the equations, in order to get:
ax=x, by=0, cx=2x and dy=5y, which ought to be solvable.
 

1. How do I find a matrix that performs a specific transformation?

To find a matrix that performs a specific transformation, you can use the process of matrix multiplication. Start by writing the transformation as a system of equations, then create a matrix using the coefficients of the variables. Multiply this matrix by the column vector representing the coordinates of a point, and the resulting output will be the coordinates of the transformed point.

2. Can I use any matrix to perform a given transformation?

No, not all matrices can perform a given transformation. The matrix must have the same number of columns as the number of dimensions in the input space and the same number of rows as the number of dimensions in the output space. Additionally, the matrix must be invertible in order to perform the inverse transformation.

3. How do I know if a matrix will perform a reflection, rotation, or translation?

The type of transformation performed by a matrix depends on its properties. A matrix that is symmetric will perform a reflection, a matrix with a determinant of 1 will perform a rotation, and a matrix with a determinant of -1 will perform a reflection and a rotation. A translation can be achieved by adding a column vector to the original matrix.

4. What is the importance of the determinant when finding a matrix?

The determinant of a matrix is important when finding a matrix because it determines whether the matrix is invertible and can perform the inverse transformation. If the determinant is 0, the matrix is not invertible and the inverse transformation cannot be performed.

5. Can I use matrix multiplication to perform multiple transformations at once?

Yes, matrix multiplication can be used to perform multiple transformations at once by multiplying the matrices representing each transformation together. The order in which the matrices are multiplied matters, as the resulting transformation will be a combination of the individual transformations. This is known as composite transformation.

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