CK12 - Geometry

Congruentanglesthat forma linearpair musteachmeasure You can use this informationto fill in
missingmeasuresin diagramsand solveproblems.

Example 1

Whatis the measureof below?

Sincethe two anglesform a linearpair, they mustsum to You can see that is a right angle

by the squaremarkingin the angle,so that anglemeasures Use subtractionto find the missingangle.

Angle will also equal becausethey are congruentlinearangles.

Example 2

Whatis the measureof below?

For now you can assumethat the interioranglesin a trianglemustsum to

(this is a fact that you haveusedin the past and we will proveit soon!).

Sinceyou may assumethat the interioranglesin a trianglemustsum to you can find if
you knowthe measuresof the othertwo angles.Use the exteriorright angleto find the measureof the interior
angleadjacentto it. The two anglestogetherare a linearpair. Sinceyou knowthat the outeranglemeasures

find the valueof the internalangleusingsubtraction.

will also equal becausethey are congruentlinearangles.Now you knowtwo of the internal

anglemeasuresin the triangle— and Use subtractionto find the measureof.