Solution:
We have 
Use the multiplication rule as follow:
From the equality of matrices we get
Therefore finally we have
Find the value of 
![\left[\begin{array}{cc} \mathrm{x} & \mathrm{y} \\ 3 \mathrm{y} & \mathrm{x} \end{array}\right]\left[\begin{array}{l} 1 \\ 2 \end{array}\right]=\left[\begin{array}{l} 3 \\ 5 \end{array}\right]](https://www.learnatnoon.com/s/wp-content/ql-cache/quicklatex.com-0863b7d782cc25f6aa50594877777cc3_l3.png "Rendered by QuickLaTeX.com")
Solution:
We have
Use the multiplication rule as follow:
From the equality of matrices we get
Therefore finally we have
