Final answer:
The perimeter of a triangle is the sum of the lengths of its three sides.
Step-by-step explanation:
The perimeter of a triangle is the sum of the lengths of its three sides. To determine the perimeter of a triangle, you need to know the lengths of its sides. If you have the lengths of the three sides, say a, b, and c, then the perimeter is given by the expression: Perimeter = a + b + c.
For example, if the lengths of the sides of a triangle are 5 cm, 7 cm, and 9 cm, then the perimeter would be: Perimeter = 5 cm + 7 cm + 9 cm = 21 cm.