If you ever see a little square at the corner of a shape, then you know that not only is this a right angle, and thus, 90 degrees, but that the two lines that form such an angle are perpendicular to one another. Squares and rectangles always have four right angles!
A right angle means that the lines will create an L or X or T when they intersect. This is exactly the definition of perpendicular, that the shapes will intersect and create at least one right angle.
