- #1

cbarker1

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I am trying to learn about the electrodynamics. I am using the textbook, Introduction to Electrodynamics (2nd Ed) by D. J. Griffiths. I am working on the Problem 1.8. The question state:

Prove that the two-dimensional rotation matrix perverse the length of A. (That is, show that $(A_y')^2+(A_z')^2=(A_y)^2+(A_z)^2$)

$\left(\begin{array}{cc} A_y'\\ A_z'\end{array}\right)$=$\left(\begin{array}{cc} cos(\phi) & sin(\phi)\\ -sin(\phi) & cos(\phi) \end{array} \right)$ $\left(\begin{array}{cc} A_y\\A_z\end{array}\right)$

I am struck at the beginning.