Asked by subash
A g.p has 8 terms.If the sum of first 4 terms is 45 and the sum of the last 4 term is 720, find the common ratio and the first term.
Answers
Answered by
Steve
S4 = a (r^4-1)/(r-1) = 45
S8 = a(r^8-1)/(r-1) = 45+720 = 765
divide and you have (r^8-1)/(r^4-1) = 765/45 = 17
r^8-1 = (r^4-1)(r^4+1)
so, r^4+1 = 17
r^4 = 16
r = ±2
Now just find a
S8 = a(r^8-1)/(r-1) = 45+720 = 765
divide and you have (r^8-1)/(r^4-1) = 765/45 = 17
r^8-1 = (r^4-1)(r^4+1)
so, r^4+1 = 17
r^4 = 16
r = ±2
Now just find a
Answered by
Favour
How did you get -+2
Answered by
Shubham
I didn't understand the 2nd line
Answered by
Ap
Op
There are no AI answers yet. The ability to request AI answers is coming soon!
Submit Your Answer
We prioritize human answers over AI answers.
If you are human, and you can answer this question, please submit your answer.