Final answer:
The formula for calculating the perimeter of a rectangle whose length is exactly twice its width is P = 6w.
Step-by-step explanation:
To calculate the perimeter of a rectangle where the length is exactly twice the width, you can use the following formula:
P = 2(l + w)
In this formula, P represents the perimeter, l represents the length, and w represents the width of the rectangle. Since the problem states that the length is exactly twice the width, you can substitute l with 2w in the formula:
P = 2(2w + w)
Simplifying this equation gives:
P = 2(3w)
P = 6w
So, the formula for calculating the perimeter of a rectangle whose length is exactly twice its width is P = 6w.