We have a diagram. We want to find the line(s) that contain point B and are perpendicular to CD. We will first extend the line to observe better.
Let's recall the definition of perpendicular lines.
Perpendicular Lines
Two coplanar lines that intersect at a right angle are said to be perpendicular lines.
Perpendicular lines create a 90^(∘) angle at their point of intersection. Notice that the lines that are perpendicular to CD are BC, AD, CG, and DH. However, we need a line that passes through point B and intersects CD at the corner of the aquarium. Therefore, among the perpendicular lines to CD, only one line fits this description and contains point B which is BC.
From here, we can conclude that there is only one line that contain point B and perpendicular to CD. This line is BC.
