LEARN MATH STEP BY STEP THROUGH VERY EASY PROCESS

GEOMETRY-TRIANGLES

__TRIANGLES __

**A closed plane figure bounded by three line
segments is called a triangle. In the figure,
ABC is a triangle bounded by three line segments AB, BC, and CA. These are called
the sides of the triangle.**

**The
points A, B, and C are called the vertices of
the triangle. The angles ∠BAC, ∠ABC,
and ∠BCA are called the interior angles or simply, the angles of the
triangle. The three sides and the three angles of a triangle are together
called the six parts (or elements) of the triangle.**

__Exterior Angles –__

**
If the
side BC or ∆ ABC is produced to the
point ‘O’ then ∠ACO is called an exterior angle of ∆ ABC at ‘C’. ∠ACB and ∠ACO are adjacent
angles. So, ∠ACB + ∠ACO = 180⁰**

**Exterior Angles + Adjacent Interior Angles = 180⁰**

**If AC is produced to D then ∠BCD will be another exterior angle of the ∆ ABC at C, being
vertically opposite angles, ∠BCD = ∠ACO.
Similarly there are two exterior angles of equal magnitude at
each vertex.**