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 2 years ago
The series a1,a2,… is a geometric progression. If a4=80 and a5=160, what is the value of a1?
 2 years ago
The series a1,a2,… is a geometric progression. If a4=80 and a5=160, what is the value of a1?

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agent0smith
 2 years 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
 2 years ago
Best ResponseYou've already chosen the best response.0\[\dfrac{160}{80} = r\]

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

agent0smith
 2 years 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
 2 years ago
Best ResponseYou've already chosen the best response.0wat value do i substitute for r?

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

agent0smith
 2 years 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
 2 years ago
Best ResponseYou've already chosen the best response.0ya.. i got it.. 10 is d ans.. thank u so much

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

agent0smith
 2 years 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.
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