How do you find the perimeter of a triangle?

The perimeter of a triangle is found by adding together the lengths of all its sides. When you denote the sides of the triangle as s1, s2, and s3, the formula expresses this relationship clearly: the perimeter is the sum of these three side lengths. This is a fundamental property of triangles and holds true for all types, whether they are scalene, isosceles, or equilateral.

The other options are formulas that apply to different shapes or contexts. For instance, the formula involving length (l) and width (w) calculates the perimeter of a rectangle. The formula that uses "3s" specifically refers to an equilateral triangle, where all sides are of equal length, but it doesn't generalize for all triangles. Lastly, "4s" is the perimeter formula for a square, which does not pertain to triangles at all. Thus, the first option captures the essence of how to calculate the perimeter of any triangle accurately.