A triangle has $$3$$ sides, $$3$$ vertices, and $$3$$ angles. A triangle whose vertices $$A$$, $$B$$, and $$C$$ referred to $$△ABC$$.

Properties of a triangle:
The first property of a triangle: $$180°$$ is always the sum of the three interior angles of a triangle.

The three angles of the $$△ABC$$ are $$∠A$$, $$∠B$$, and $$∠C$$.

As per the property, the sum of the three angles of the $$△ABC$$ is $$180°$$.

That is, $$∠A + ∠B + ∠C = 180°$$.
The second property of a triangle: The sum of the length of a triangle's two sides is always greater than the length of the triangle's third side.

The three sides of the $$△ABC$$ are $$AB$$, $$BC$$ and $$AC$$.

As per the property, the sum of the length of any two sides of an $$△ABC$$ is always greater than the length of the third side of the $$△ABC$$.

Let the two sides are $$AB$$ and $$BC$$, and the third side is $$AC$$.

Thus, we have $$AB + BC > AC$$.

Similarly,

$$BC + AC > AB$$ or

$$AB + AC > BC$$.