Answer:
The rungs are perpendicular to the other side.
Explanation:
Given
The sides of ladder are parallel.Rungs is perpendicular to one side of the ladder.
Let


When two lines are parallel then the slopes of two lines are equal.
We can say

Where
= slope of line a( side of ladder)
= solpe of line b( side of ladder)
When two lines are perpendicular then slopes of two lines are opposite reciprocal to each other.
We can say

Where
= Slope of line b
=Slope of line c (rung)
By transitive property of equality we get

Hence, the slope of side of ladder a and rung c are opposite reciprocal to each other.Therefore , the rungs are perpendicular to the other side.