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Problem 922
922
The circumference round the trunk of a large tree is measured and found to be 5.00 m. After one year the circumference is measured again and found to be 5.02 m.
Given instead that the circumferences at yearly intervals form a geometric progression, find the circumference 20 years after the first measurement.
Solution
The initial circumference is 5.00 m, and after one year it is 5.02 m. We assume the circumferences form a geometric progression.
The common ratio, \(r\), is calculated as:
\(r = \frac{5.02}{5} = 1.004\)
To find the circumference 20 years after the first measurement, we use the formula for the \(n\)-th term of a geometric progression:
\(a_n = a_1 imes r^{n-1}\)
Here, \(a_1 = 5.00\), \(r = 1.004\), and \(n = 21\) (since we want the circumference after 20 years, starting from the first measurement):