Triangles are either contracting (boundary lines converge) or expanding (boundary lines diverge). Contracting triangles: symmetrical, ascending, descending. Expanding triangles are rare and have specific characteristics.
Description
The boundary lines of a triangle either converge toward an apex (contracting triangles) or diverge (expanding triangles). Contracting triangles have three subtypes based on whether the converging lines are horizontal, angled up, or angled down. Expanding triangles are rare.
Key Points
- Contracting symmetrical: both boundary lines slope toward apex (most common triangle type)
- Contracting ascending: lower boundary is flat or rising; upper boundary is declining
- Contracting descending: upper boundary is flat or declining; lower boundary is rising
- Expanding (reverse symmetrical): boundary lines diverge — each sub-wave is larger than the prior one
- Barrier triangle: one boundary line is horizontal; the other converges toward it
- Expanding triangles: wave 3 is not the shortest; boundary lines diverge — very rare
