# How do you find the first term of the arithmetic sequence having the data given #S_n= 781#, d = 3, n = 22?

##### 1 Answer

Mar 21, 2016

#### Answer:

Use the formula

#### Explanation:

a is the first term.

**Practice exercises:**

An arithetic sequence of 14 terms has a sum of -322. The first term is -2. Find the common ratio, r.

Good luck.