7th Grade · Geometry
Valid Triangle
7.G.A.2
Definition
A triangle whose side lengths satisfy the Triangle Inequality Theorem (the sum of any two sides exceeds the third). All three checks must pass.
Teach it
Where it is taught, with guided notes, practice, homework, an exit ticket and an interactive Teacher Deck.
Examples
- Sides 5, 8, 10: 5+8 = 13>10, 5+10 = 15>8, 8+10 = 18>5 — all pass, valid triangle.
- Sides 4, 6, 7: check smallest pair 4+6 = 10>7 — valid.
Key rule
If the shortest two sides sum to more than the longest side, it's valid — only need to check once.
Memory hook
Smallest two sides beat the biggest one? Valid.