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The Included Angle

Part of the Congruence & Proof section of Coddy's Geometry journey. Lesson 16 of 63.

Two sides of a triangle meet at a corner. The angle at that corner, the one the two sides make with each other, is called the included angle of those sides: it is included between them.

$Triangle ABC with ticks on AB and BC and an arc at B$

Here sides AB and BC meet at B, so their included angle is ∠ABC. The other two angles, at A and at C, each touch only one of the two sides. A quick test: the included angle's vertex is the letter the two side names share. AB and BC share B.

Challenge

Tap the included angle of sides ST and SU in triangle STU, then press Check.

Try it yourself

$Find the right part on the figure$

Find the right part on the figure

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Congruence & Proof

2Congruent Triangles

Same Size, Same Shape Matching Sides Matching Angles What Congruence Gives Recap: Matching Parts

5ASA and AAS

The Side Between The ASA Rule The AAS Rule ASA or AAS?Recap: ASA and AAS

8Proofs with Vertical Angles

Vertical Angles in Proofs The Bowtie Bowtie with ASA Linear Pairs in Proofs Recap: Vertical Angles

11Similarity Proofs

AA Similarity Two Right Triangles SSS Similarity SAS Similarity Similar, Then Find Recap: Similarity