What you’ll learn
Understand triangle angle sum.
Key idea
A nondegenerate triangle has positive interior angles whose total is a straight angle.
Positive individual angle bounds do not suffice; the complete nondegenerate triple must sum to 180.
Worked example
Classify examples and non-examples for the concept 'Understand triangle angle sum'.
Classify whether 25,35,130 degrees can be one triangle's interior angles, with total-angle evidence.
- A triangle's three interior angles sum to 180 degrees; missing third angle=180-25-35=120.
- The proposed triple 25,35,130 totals 190; positive individual angles alone are insufficient.
Answer: False — total is 190 degrees, not equal to 180.
Quick Check
Classify examples and non-examples for the concept 'Understand triangle angle sum'.
Classify whether 35,30,115 degrees can be one triangle's interior angles, with total-angle evidence.