90 degree clockwise rotation is described by the matrix,
[tex]\begin{bmatrix}0&1\\-1&0\\ \end{bmatrix}[/tex]
If you apply the matrix to the vector [tex]B[/tex] you get,
[tex]\begin{bmatrix}0&1\\-1&0\\ \end{bmatrix}\begin{bmatrix}7\\8\\ \end{bmatrix}=\begin{bmatrix}7\cdot0+8\cdot1=8\\ -1\cdot7+8\cdot0=-7\\ \end{bmatrix}[/tex]
So false.
Hope this helps.
