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

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agent0smithBest 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.
 one year ago

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

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

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

agent0smithBest ResponseYou've already chosen the best response.1
You can find a1 by either just dividing by r until you reach a1, or using \[\large a _{4} = 80 = a _{1} r ^{41} \] \[\large a _{5} = 160 = a _{1} r ^{51} \]
 one year ago

arun8408Best ResponseYou've already chosen the best response.0
wat value do i substitute for r?
 one year ago

agent0smithBest ResponseYou've already chosen the best response.1
\[\large r = \frac{ a _{5} }{ a _{4} }\]
 one year ago

agent0smithBest ResponseYou've already chosen the best response.1
r should be 2, 160/80 = 2 \[\large a _{4} = 80 = a _{1} * 2 ^{41}\] \[\large 80 = a _{1}*2 ^{3}\]
 one year ago

arun8408Best ResponseYou've already chosen the best response.0
ya.. i got it.. 10 is d ans.. thank u so much
 one year ago

arun8408Best ResponseYou've already chosen the best response.0
What comes next in this sequence: 1,2,6,24,120,−−?
 one year ago

agent0smithBest ResponseYou've already chosen the best response.1
There'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.
 one year ago
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