How do you write an nth term rule for r=6 and a_3=72?

2 Answers
Mar 22, 2018

Un= 2*6^(n-1)

Explanation:

As we know that 72 is the third term and the common ratio is 6 so therefore we will divide 72 by 6 and then again by 6 in order to get the 1st term which is 2. Or in other terms if we do 6^2 which is 36, then you divide 72 by 36 which will give you 2.

Then you insert the formula in the geometric series which is written above as the answer

a_n=2xx(color(red)(6))^(n-1)

Explanation:

"the nth term of a geometric sequence is"

•color(white)(x)a_n=ar^(n-1)

"where a is the first term and r the common ratio"

"we are given r and require to find a"

rArra_3=a(6)^2=72larrcolor(blue)"n th term formula"

rArr36a=72rArra=72/36=2

rArra_n=2xx(6)^(n-1)larrcolor(blue)n^(th) " term rule"