Theory:

A triangle has three sides, three vertices, and three angles. A triangle with vertices \(A\), \(B\), and \(C\) is denoted as \(△ABC\).
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Properties of a triangle:
 
The first property of a triangle: The sum of the three interior angles of a triangle is always \(180°\).
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\(∠A + ∠B + ∠C = 180°\).
 
The second property of a 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.
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\(AB + BC > AC\) or \(BC + AC > AB\) or \(AB+ AC > BC\).