Final answer:
The perimeter of a triangle with side lengths of 9.8, 4.6mn, and 12.1 is found by adding all the sides together, resulting in an expression 21.9 + 4.6mn. The correct option is a.
Step-by-step explanation:
The perimeter of a triangle with side lengths of 9.8, 4.6mn, and 12.1 can be found by simply adding all the side lengths together. Since the perimeter is the total distance around the triangle, we use the formula for the perimeter of a triangle:
Perimeter = side1 + side2 + side3
Plugging in the given side lengths:
Perimeter = 9.8 + 4.6mn + 12.1
Combine like terms:
Perimeter = 21.9 + 4.6mn
Therefore, the correct option is a. 21.9 + 4.6mn.