*Isosceles
Trapezoid
I have:
 only one set of parallel sides
 base angles congruent
 legs congruent
 diagonals congruent
 opposite angles supplementary 

Theorems: 
1.
A trapezoid is isosceles if and only if the base angles are
congruent.

2.
A trapezoid is isosceles if and only if the
diagonals are congruent.

3. If a trapezoid is
isosceles, the opposite angles are supplementary.

Never assume that a trapezoid is isosceles unless
you are given (or can prove) that information.

