8th Grade · Geometry
Acute / Obtuse
8.G.B.6
Definition
A triangle is classified by comparing the sum of the squares of the two shorter sides to the square of the longest side. Greater means acute, less means obtuse, equal means right.
Teach it
Where it is taught, with guided notes, practice, homework, an exit ticket and an interactive Teacher Deck.
Examples
- Sides 4,5,6: 16+25 = 41 > 36 — acute.
- If a2+b2 = c2, the triangle is right.
Key rule
Plug the longest side in as c, then compare a2+b2 to c2.
Memory hook
Compare the squares to classify the triangle.