CK12 - Geometry

below.

Whatis the measureof angleADC?

This problemrequirestwo stepsto solve.You alreadyknowthat baseanglesin an isoscelestrianglewill
be congruent,but you needto find the relationshipbetweenadjacentanglesas well. Imagineextendingthe

parallelsegments and on the trapezoidand the transversal. You’ll noticethat the angle

labeled is a consecutiveinterioranglewith.

Consecutiveinterioranglesalongtwo parallellineswill be supplementary. You can find by

subtracting from.

So, measures. Since is adjacentto the samebaseas in an isosceles

trapezoid,the two anglesmustbe congruent.Therefore,

Hereis a proofof this property.

• Given:Isoscelestrapezoid with and


• Prove: