+0  
 
0
133
2
avatar

the first term of a geometric series is 1,the nth term is 128 and the sum of the n terms is 256 find the common ratio and the number of terms.

Guest Jul 4, 2017
Sort: 

2+0 Answers

 #1
avatar
0

lets call the ratio q, ok?

 

the sum of the first term+the second term+.....+the nth term=a1*(qn-1)/(q-1). a1=1, so the sum=(qn-1)/(q-1). we know the nth term is 128, so qn-1=128, so qn=128*q

 

128*q-1/q-1=256

 

 

128*q-1=256*q-256

 

 

-1=128*q-256

 

128*q=255

 

q=255/128

 

the series is impossible

Guest Jul 4, 2017
 #2
avatar+26322 
+1

I suspect the sum should be 255, rather than 256. If so everything works out nicely!

Alan  Jul 4, 2017

8 Online Users

avatar
We use cookies to personalise content and ads, to provide social media features and to analyse our traffic. We also share information about your use of our site with our social media, advertising and analytics partners.  See details