Given: Trapezoid ABCD, BC || AD, EB=EC

Prove: ABCD is isosceles

<A = <D
Definition
BC || AD, EB=EC
ABCD is isosceles
<EBC = <A and <ECB = <D
Parallel lines form equal corresponding angles
<EBC = <ECB
Substitution
Given
If two sides of a triangle are equal, the angles opposite them are equal