Recall the following information:
1) In a plane, two lines that are parallel exist on the same axis.
2) Hence, any line which is perpendicular to one of two parallel lines is also perpendicular to the other.
3) This concept is evident in the model of ladders, where each of the vertical lines is perpendicular to the parallel step lines(horizontal lines).
With this information, it can be said that if a line is perpendicular to one of two parallel lines, then it is perpendicular to the other.
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