# How do you find the formula for #a_n# for the arithmetic sequence #a_1=5, a_4=15#?

##### 1 Answer

Aug 9, 2017

#### Answer:

#### Explanation:

#"the nth term of an arithmetic sequence is "#

#•color(white)(x)a_n=a_1+(n-1)d#

#"where d is the common difference"#

#"given "a_4=15" and "a_1=5#

#rArr5+3d=15rArrd=10/3#

#rArra_n=5+10/3(n-1)#

#color(white)(rArra_n)=5+10/3n-10/3#

#color(white)(rArra_n)=10/3n+5/3#