Let the products produced in the first year be X, then x( 1+P 1) in the second year, X (1+P1) in the third year and X (1+P2) in the fourth year.

And p is the annual growth rate, knowing that the fourth year should be x( 1+P)?

From these two fourth-year values, we know that

x( 1+P)？ = x( 1+p 1)( 1+P2)( 1+P3)

( 1+P)？ =( 1+p 1)( 1+P2)( 1+P3)①

And P 1+P2+P3 is a constant value.

Here, we need to use the mean inequality in the form of x+y≥2√xy, the generalization of x+y+z≥3, and the square root xyz.

So the formula ① here is ≤(3+P 1+P2+P3 /3)?

1+P≤ 1+(P 1+P2+P3)/3

The maximum value is P 1+P2+P3/3.