# How do you use the geometric mean to find the 7th term in a geometric sequence if the 6th term is 6 and the 8th term is 216?

##### 1 Answer

Nov 19, 2015

Find that

#### Explanation:

The general term of a geometric sequence can be written:

#a_n = a r^(n-1)#

where

So

So we find:

#a_7 = a r^6 = sqrt(a r^6 * a r^6) = sqrt(a r^5 * a r^7) = sqrt(a_6 a_8)#

That is:

In other words,

In our particular example

So:

#a_7 = sqrt(a_6 a_8) = sqrt(6*6^3) = sqrt(6^2*6^2) = 6^2 = 36#