Hello, watcher!

You're expected to know this formula . . .There is an arithmetic sequence such that the 7th term minus the 4th term is 12

and the sum of the 7th term and 4th terms is -28.

Obtain the closed form of the sequence and write down the 10th and 20th terms.

The term is: .

. . where is the first term, and is the common difference.

The term is: .

The term is: .

Their difference is 12: .

Their sum is -28: .

. . Substitute [1] into [2]: .

Hence, the term is: .

The term is: .

The term is: .