__Triangles__

**A triangle is a three-sided polygon. It is the polygon with the least
number of sides.**

**It is denoted by the symbol ∆.**

**We see many triangle shaped objects in our daily life.**

**Example: Draw a rough sketch of a triangle ABC. Mark a point P in
its interior and a point Q in its exterior. Is the point A in its exterior
or in its interior?**

**Point A is not in the interior or exterior of ∆ ABC as it is a vertex (a
point where two line segments meet).**

**Example:
a) Identify three triangles in the figure.
b) Write the names of seven angles.
c) Write the names of six line segments.
d) Which two triangles have ∠B as common?**

**a) The three triangles are ∆ABC, ∆ABD and ∆ACD
b) The angles are ∠BAC, ∠BAD, ∠DAC, ∠ABD, ∠ACD, ∠ADB and
∠ADC.
c) The line segments are AB, BC, CA, BD, DC and AD.
d) ∆ABC and ∆ABD have ∠B as common.**