A community for students. Sign up today!
Here's the question you clicked on:
 0 viewing
 one year ago
The series a1,a2,… is a geometric progression. If a4=80 and a5=160, what is the value of a1?
 one year ago
The series a1,a2,… is a geometric progression. If a4=80 and a5=160, what is the value of a1?

This Question is Closed

agent0smith
 one year ago
Best ResponseYou've already chosen the best response.1\[\large a _{n} = a _{1} r ^{n1} \] is the formula for a geometric progression, r being the common ratio, and a1 being the first term, an being the nth term. r is the common ratio, so if you divide a5 by a4, you'll find r. Then you can use \[\large a _{4} = 80 = a _{1} r ^{41}\] to find a1.

ParthKohli
 one year ago
Best ResponseYou've already chosen the best response.0\[\dfrac{160}{80} = r\]

AravindG
 one year ago
Best ResponseYou've already chosen the best response.0nth term of a GP= ar^{n1} use this and write the 5th and 4th terms ,you can solve them

ParthKohli
 one year ago
Best ResponseYou've already chosen the best response.0\[r = 2\]You can now easily determine the first term by continuous division.

agent0smith
 one year ago
Best ResponseYou've already chosen the best response.1You can find a1 by either just dividing by r until you reach a1, or using \[\large a _{4} = 80 = a _{1} r ^{41} \] \[\large a _{5} = 160 = a _{1} r ^{51} \]

arun8408
 one year ago
Best ResponseYou've already chosen the best response.0wat value do i substitute for r?

agent0smith
 one year ago
Best ResponseYou've already chosen the best response.1\[\large r = \frac{ a _{5} }{ a _{4} }\]

agent0smith
 one year ago
Best ResponseYou've already chosen the best response.1r should be 2, 160/80 = 2 \[\large a _{4} = 80 = a _{1} * 2 ^{41}\] \[\large 80 = a _{1}*2 ^{3}\]

arun8408
 one year ago
Best ResponseYou've already chosen the best response.0ya.. i got it.. 10 is d ans.. thank u so much

arun8408
 one year ago
Best ResponseYou've already chosen the best response.0What comes next in this sequence: 1,2,6,24,120,−−?

agent0smith
 one year ago
Best ResponseYou've already chosen the best response.1There's a pattern: first term: 1x1 = 1 second term: 2x1 = 2 third term: 3x2 = 6 fourth term: 4x6 = 24 fifth term: 5x24 = 120 sixth term: ? x120 = ? Look at the pattern of multiples on the left.
Ask your own question
Ask a QuestionFind more explanations on OpenStudy
Your question is ready. Sign up for free to start getting answers.
spraguer
(Moderator)
5
→ View Detailed Profile
is replying to Can someone tell me what button the professor is hitting...
23
 Teamwork 19 Teammate
 Problem Solving 19 Hero
 Engagement 19 Mad Hatter
 You have blocked this person.
 ✔ You're a fan Checking fan status...
Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.