What you’ll learn
Use ASA.
Key idea
ASA uses the side between the two known angles; a nonincluded side gives a different criterion.
The included side joins both known angle vertices; error cases must not import an unsupplied base length.
Worked example
Enter the exact value or ordered values in the format requested below.
Correspondence A-D, B-E, C-F; angles A=D=B=E=30 degrees. Included sides AB=DE=5. Use ASA and find corresponding F in degrees.
- The included AB=DE=5 joins the known angle vertices, establishing ASA.
- Third angles C/F=180-2(30)=120 degrees; missing included DE must match AB=5.
Answer: 120
Quick Check
Evaluate a worked attempt at use asa, identify the first invalid step, and provide the correction.
Correspondence A-D, B-E, C-F; angles A=D=B=E=30 degrees. Only side AC=DF=2 is supplied. Student: Step 1, two angle pairs and a side pair match. Step 2, AC/DF are the included sides between A/B and D/E, so this is ASA. Identify first invalid step and repair the criterion.