# How do I find the sum of the arithmetic sequence 3, 5, 7, 9, ..., 21?

##### 2 Answers

Jul 11, 2018

#### Explanation:

Given arithmetic sequence

The first term

If there are

hence the sum of given arithmetic progression (

Jul 11, 2018

#### Explanation:

#"the sum to n terms of an arithmetic sequence is"#

#â€¢color(white)(x)S_n=n/2[2a+(n-1)d]#

#"where a is the first term and d the common difference"#

#"here "a=3,d=7-5=5-3=2,n=10#

#S_(10)=5[(2xx3)+(2xx9)]#

#color(white)(xx)=5(6+18)=120#