Final answer:
The farmer can calculate the area of the field after t years by using the formula A = (40 + 3t)², which accounts for the annual increase in each side's length. This results in A = 1600 + 120t + 9t² square meters.
Step-by-step explanation:
To calculate the area, A, of the farmer's square field after t years, we need to account for the annual extension of each side by 3 meters. Initially, each side of the field is 40 meters. After t years, each side will be (40 + 3t) meters long. The formula for the area of a square is side length squared, so:
A = (side length) · (side length)
Therefore, the area of the field after t years is:
A = (40 + 3t)² = (40 + 3t) · (40 + 3t)
Expanding this, we have:
A = 1600 + 120t + 9t² square meters
This quadratic equation represents the growing area of the field in square meters as a function of time, t, in years.