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2. Place a ruler along BC
3. Place a set square on the ruler
4. Slide the set square until it touches vertex A
5. Draw a perpendicular line from A to BC
This perpendicular line is the altitude

Diagram 4: Construction Using Set Square.

Special Observation

Can a side of a triangle be an altitude?

Yes.
This happens in a right-angled triangle, where one side is perpendicular to another.

Applications in Real Life

• Measuring height of structures
• Construction and architecture
• Designing slopes and supports
Altitudes help in accurate measurement and design

Summary – Key Points
• Triangles can be constructed using:
• Two sides and included angle (SAS)
• Two angles and included side (ASA)
• Triangle exists only if angle conditions are satisfied
• Sum of angles in a triangle is always 180°
• Third angle can be calculated without construction
• Angles control the shape and formation of triangle
• An altitude is a perpendicular from a vertex to the opposite side
• A triangle has three altitudes
• Altitudes may lie inside or outside the triangle
• Set square ensures accurate perpendicular construction
• In right triangles, a side can act as an altitude
• Altitude represents the height of a triangle