Question

Reflect the given triangle over the line y=x. [3 6 3 -3 3 3]

Answer 1

If reflected over y = x

then use

$\left[\begin{array}{ccc}0&1\\1&0\end{array}\right]$

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$\left[\begin{array}{ccc}0&1\\1&0\end{array}\right] \left[\begin{array}{ccc}3&6&3\\-3&3&3\end{array}\right]$

similar as (x, y) → (y, x)

multiply the matrixes to get the final answer

$\left[\begin{array}{ccc}(3*0+1*-3)&(6*0+1*3)&(3*0+1*3)\\(3*1+(-3*0)&(1*6+0*3)&(1*3+0*3)\end{array}\right]$

$\left[\begin{array}{ccc}-3&3&3\\3&6&3\end{array}\right]$