if ~ defines an equvalence relation on A then the set of equivalence classes of ~ form a partition of A

This is different from the first one can someone me

Use sigma notation to represent the following series for 9 terms.

Frank is lending $1,000 to sarah for two years. frank and sarah agree that frank should earn a real return of 4 percent per year. instructions: a. the cpi (times 100) is 100 at the time that frank makes the loan. it is expected to be 113 in one year and 127.7 in two years. what nominal rate of interest should frank charge sarah?