Chapter 1.8, Problem 49E

In a sentence, describe the geometric effect of multiplying a vector x by the matrix

$A=\left[\begin{array}{l}{\cos }^2\theta -{\sin }^2\theta -2\sin \theta \cos \theta \\ 2\sin \theta \cos \theta {\cos }^2\theta -{\sin }^2\theta \end{array}\right]$