Nothing.
A perpendicular is an adjective, not a noun. A perpendicular, by itself, cannot exist. A perpendicular bisector, for example, does not have any sides.
it's a something
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They look like an upside-down "T".
A perpendicular bisector has a right angle or 90 degrees
Perpendicular is when two lines cross and form a right angle, which I hope you know what that is.
Perpendicular bisector.
As far as we know, two lines can be perpendicular, or they can be parallel, but they can't be both.
It looks like an upside-down "T".
it would look weird because that is not possible
Is a line that bisects a side of a triangle and is perpendicular to that side.
A perpendicular bisector
It looks like a plus sign (+)