Question

A equation for the ninth term of a arithmetic sequence who seventh term is 21 and common difference of 5

Answer 1

`9th=31`

Explanation:

From the question we are told that:

Seventh term
`7th= 21`

Common difference
`d= 5`

Generally Equation for seventh term

`7th=a+(7-1)d`

Therefore the First Term is given as

`a=7th-(7-1)d`

`a=21-6*5\\a=-9`

Generally the equation for 9th term is mathematically given by

`9th=a+8d`

`9th=-9+8(5)`

`9th=31`