+0  
 
0
89
2
avatar

Determine the number of terms n in the arithmetic sequence.

 

a1 = 9, an = 72, Sn = 405

 Jun 4, 2021
 #1
avatar
0

I'm a little confused on the question, or it just may be I'm not smart enough to understand..

 Jun 4, 2021
 #2
avatar+114438 
+1

It has nothing to do with intelligence,  most likely you have not learned it yet.

It is a topic called sequences and series.

 

Let me see.

AP

a=9

 

Tn=a+(n-1)d = 72

so

9+(n-1)d=72

 

Sn=n/2(a+Tn) = 405

n/2 * (9+72) =405

n/2 * 81 = 405

n=10

 Jun 4, 2021

32 Online Users

avatar