The equation could be used to calculate the sum of the geometric series is 
<h3>Sum of geometric sequence</h3>
Geometric sequence are sequence that increase expoentially. The formula for calculating the sum of an exponential sequence is expressed as:

where
- a is the first term
- n is the number of terms
- r is the common ratio
From the given sequence
a= 1/3
r = 2/9 * 3 = 2/3
Substitute into the formula

Hence the equation could be used to calculate the sum of the geometric series is 
Learn more on geometric series here; brainly.com/question/24643676
Answer:
u=5.23
Step-by-step explanation:
