Home » mcq » Linear Algebra » The transformation matrix for mirroring a point in x-y plane about the line y = x is given by A. \[\left[ {\begin{array}{*{20}{c}} { – 1}&0 \\ 0&1 \end{array}} \right]\] B. \[\left[ {\begin{array}{*{20}{c}} 0&1 \\ 1&0 \end{array}} \right]\] C. \[\left[ {\begin{array}{*{20}{c}} 0&{ – 1} \\ { – 1}&0 \end{array}} \right]\] D. \[\left[ {\begin{array}{*{20}{c}} 1&0 \\ 0&{ – 1} \end{array}} \right]\]
The transformation matrix for mirroring a point in x-y plane about the line y = x is given by A. \[\left[ {\begin{array}{*{20}{c}} { – 1}&0 \\ 0&1 \end{array}} \right]\] B. \[\left[ {\begin{array}{*{20}{c}} 0&1 \\ 1&0 \end{array}} \right]\] C. \[\left[ {\begin{array}{*{20}{c}} 0&{ – 1} \\ { – 1}&0 \end{array}} \right]\] D. \[\left[ {\begin{array}{*{20}{c}} 1&0 \\ 0&{ – 1} \end{array}} \right]\]
The correct answer is $\boxed{\left[ {\begin{array}{*{20}{c}} { – 1}&0 \ 0&1 \end{array}} \right]}$.
A transformation matrix is a matrix that describes how a geometric object is transformed under a certain transformation. In this case, the transformation is mirroring a point in the $x$-$y$ plane about the line $y=x$.
To find the transformation matrix, we can use the following steps:
Find the vector that represents the line $y=x$. This vector is $(1,1)$.
Find the normal vector to the line $y=x$. This vector is $(-1,0)$.
Take the dot product of the two vectors. This gives us the determinant of the transformation matrix, which is $-1$.
The transformation matrix is then given by $\left[ {\begin{array}{*{20}{c}} { – 1}&0 \
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0&1 \end{array}} \right]$.
The other options are incorrect because they do not represent the correct transformation. Option A is the identity matrix, which does not change the position of any points. Option B is the matrix that represents a rotation of 90 degrees counterclockwise around the origin. Option C is the matrix that represents a reflection across the $y$-axis. Option D is the matrix that represents a reflection across the $x$-axis.