\textbf{131-} The images of points $A(2,4)$ and $B(-6,2)$ under the transformation $D(x,y) = \left(-\dfrac{1}{2}y,\ \dfrac{1}{2}x+1\right)$ are called $A'$ and $B'$. What is the angle between lines $AB$ and $A'B'$?
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(1) $30°$ \hfill (2) $60°$ \hfill (3) $90°$ \hfill (4) $180°$
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