### Theory:

A triangle has three sides, three vertices, and three angles. A triangle with vertices $$A$$, $$B$$, and $$C$$ is denoted as $$△ABC$$.

Properties of a triangle:
• The sum of the three interior angles of a triangle is always $$180°$$.
• The sum of the length of two sides of a triangle is always greater than the length of the third side.
The first property of the triangle: The sum of the three interior angles of a triangle is always $$180°$$.
$$∠A$$ $$+$$ $$∠B$$ $$+$$ $$∠C$$ $$=$$ $$180°$$.
The second property of triangle: The sum of the length of two sides of a triangle is always greater than the length of the third side of a triangle.

$$AB + BC > AC$$ or $$BC + AC > AB$$ or $$AB+ AC > BC$$.