The parallel sides of a trapezoid are called
bases. The angles
that share a base as a common side are called a pair of base angles.
If the sides of a trapezoid that are not parallel are
exactly the same length, the trapezoid is said to be isosceles. Where have you seen
that term before? Compare the base angles of an isoceles trapezoid. Now look at
the diagonals of an isoceles trapezoid. Compare their lengths.
Trapezoidal shapes are often used in building arches, where
each block or stone supports, and is supported by, the pieces above and below
it. Another use is in binoculars in which the magnifying lenses invert the
image. Trapezoidal prisms are used to turn the inverted images right side up