To convert the given exponential growth formula from a decade-based increment to a 2-year increment, you need to determine the growth rate over 2 years.
The original formula is:
\[ p(d) = 1,000,000(1 + 0.15)^d \]
Where \( d \) is the number of decades. Since a decade consists of 10 years, we first need to find the equivalent growth factor for 2 years.
The growth factor for 10 years (1 decade) is \( 1 + 0.15 = 1.15 \).
To find the growth factor for 2 years, you can take the 10-year growth factor and raise it to the power of \(\frac{2}{10}\) (which is the fraction of the decade that 2 years represents):
\[
\text{Growth factor for 2 years} = (1.15)^{\frac{2}{10}} = (1.15)^{0.2}
\]
Now we need to calculate this value:
\[
1.15^{0.2} \approx 1.02899 \text{ (or roughly 1.029)}
\]
Now, we can express the population growth based on 2-year increments. The number of 2-year increments in \( d \) decades is \( 5d \) (since there are 5 sets of 2 years in a decade).
Thus, the population formula that incorporates 2-year increments becomes:
\[
p(n) = 1,000,000(1.15^{0.2})^n
\]
Where \( n \) is the number of 2-year increments. Simplifying gives us:
\[
p(n) = 1,000,000 (1.029)^n
\]
This formula can now be used to predict the city's population growth every 2 years based on the initial population of 1,000,000 and the growth factor for 2 years.