CK12 - Geometry

4. AngleAdditionPostulate
   5. Substitution


5. Given
   7. Substitution

Subtract fromboth sides(Re-

minder:Anglemeasuresare all real num-

8.

bers,so propertiesof qualityapply.)

9. Definitionof congruentangles

This is the end of the proof.The last statementis the requirementmadein the proveabove.This is the
signalthat the proofis completed.

LessonSummary

In this sectionyou haveseentwo examplesillustratingthe formatof two-columnproofs.The formatof two-
columnproofsis the sameregardlessof the specificdetails.Geometryoriginatedmanycenturiesago using
this samekind of deductivereasoningproof.

Pointsto Consider

You will see and writemanytwo-columnproofsin futurelessons.The frameworkwill stay the same,but the
detailswill be different.Someof the statementsthat we proveare importantenoughthat they are identified
by the nametheorem.You will learnaboutmanytheoremsand use themin proofsand problemsolving.

LessonExercises

Use the diagrambelowto answerquestions1-10.

Whichof the followingcan be assumedto be true from the diagram?Answeryes or no.

1.

2.

3.

4.

5.