TriangleSumTheoremThe sum of the measuresof the interioranglesin a triangleis
180°Regardlessof whetherthe triangleis right,obtuse,acute,scalene,isosceles,or equilateral,the interiorangles
will alwaysadd up to Examineeachof the trianglesshownbelow.
Noticethat eachof the triangleshas an anglethat sumsto
You can also use the trianglesum theoremto find a missinganglein a triangle.Set the sum of the angles
equalto and solvefor the missingvalue.
Example 2
Whatisin the trianglebelow?
Set up an equationwherethe threeanglemeasuressum to Then,solvefor.Now that you haveseenan exampleof the trianglesum theoremat work,you may wonder, why it is true.
The answeris actuallysurprising:The measuresof the anglesin a triangleadd to becauseof the