Given that:
angle 1 is congruent to angle 3 and angle 2 is congruent to angle 4, we can say that AB and AC should be perpendicular. That's because:
[tex]\begin{gathered} \measuredangle1+\measuredangle2+\measuredangle3+\measuredangle4=180 \\ \to2\measuredangle1+2\measuredangle2=180 \\ \measuredangle1+\measuredangle2=90 \\ (\measuredangle1=\measuredangle3),\text{ so} \\ \measuredangle2+\measuredangle3=90 \end{gathered}[/tex]
As the angle between the lines is 90°, they are perpendicular. So,
