Move to the next side (in whichever direction you want to move), which will sweep up an included angle. Notice we are not forcing you to pick a particular side, because we know this works no matter where you start. The SAS Postulate says that triangles are congruent if any pair of corresponding sides and their included angle are congruent. Here, instead of picking two angles, we pick a side and its corresponding side on two triangles. SAS theorem (Side-Angle-Side)īy applying the Side Angle Side Postulate (SAS), you can also be sure your two triangles are congruent. You will see that all the angles and all the sides are congruent in the two triangles, no matter which ones you pick to compare. So go ahead look at either ∠C and ∠T or ∠A and ∠T on △CAT.Ĭompare them to the corresponding angles on △BUG. The postulate says you can pick any two angles and their included side. You may think we rigged this, because we forced you to look at particular angles. You can only make one triangle (or its reflection) with given sides and angles. This is because interior angles of triangles add to 180°.
This forces the remaining angle on our △CAT to be:ġ80 ° − ∠ C − ∠ A 180°-\angle C-\angle A 180° − ∠ C − ∠ A The two triangles have two angles congruent (equal) and the included side between those angles congruent. See the included side between ∠C and ∠A on △CAT? It is equal in length to the included side between ∠B and ∠U on △BUG. Notice that ∠C on △CAT is congruent to ∠B on △BUG, and ∠A on △CAT is congruent to ∠U on △BUG. In the sketch below, we have △CAT and △BUG. An included side is the side between two angles. The Angle Side Angle Postulate (ASA) says triangles are congruent if any two angles and their included side are equal in the triangles. Triangle Congruence Postulates and Theorems ASA theorem (Angle-Side-Angle) Let's take a look at the three postulates abbreviated ASA, SAS, and SSS. Testing to see if triangles are congruent involves three postulates. More important than those two words are the concepts about congruence. Do not worry if some texts call them postulates and some mathematicians call the theorems.
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