Answer
Rotation by $90$ degrees counterclockwise
Work Step by Step
The matrix of the initial triangle's coordinates is:
$B=\begin{bmatrix}0&2&2\\0&0&-4\end{bmatrix}$
Consider matrix $A$:
$A=\begin{bmatrix}0&-1\\1&0\end{bmatrix}$
Compute $AB$:
$AB=\begin{bmatrix}0&-1\\1&0\end{bmatrix}\begin{bmatrix}0&2&2\\0&0&-4\end{bmatrix}$
$=\begin{bmatrix}0+0&0+0&0+4\\0+0&2+0&2+0\end{bmatrix}$
$=\begin{bmatrix}0&0&4\\0&2&2\end{bmatrix}$
We notice that the new triangle is the initial triangle rotated by $90$ degrees counterclockwise.
