Which best describes the relationship between the successive terms in the sequence shown?
2 answers:
Given series is 2.4,-4.8,9.6,-19.2
To find whether it has common difference or common ratio let us find few differences and few ratios of consecutive terms.
Common difference of first 2 terms = 2nd term - first term = -4.8-2.4 = -7.2
Common difference of 2nd and 3rd terms = 3rd term - 2nd term = 9.6-(-4.8) = 14.4
Since those common differences are not equal the given series does not have common difference at all.
To check if it has common ratio or not let us find few ratios of consecutive terms.
Common ratio of first 2 terms = =
Common ratio of 2nd and 3rd terms =
So, the given series has common ratio as -2.0
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Let n and d represent the numerator and denominator of the fraction.
.. (n +1)/(d +1) = 4/5
.. (n -5)/(d -5) = 1/2
Eliminating fractions from these equations gives
.. 5(n +1) = 4(d +1)
.. 2(n -5) = (d -5)
Subtracting the first equation from 4 times the second gives
.. 4(2(n -5)) -(5(n +1)) = 4(d -5) -(4(d +1))
.. 8n -40 -5n -5 = 4d -20 -4d -4
.. 3n = 21
.. n = 7
.. 2(7 -5) = d -5
.. 9 = d
The fraction is 7/9.
.. (n +1)/(d +1) = 4/5
.. (n -5)/(d -5) = 1/2
Eliminating fractions from these equations gives
.. 5(n +1) = 4(d +1)
.. 2(n -5) = (d -5)
Subtracting the first equation from 4 times the second gives
.. 4(2(n -5)) -(5(n +1)) = 4(d -5) -(4(d +1))
.. 8n -40 -5n -5 = 4d -20 -4d -4
.. 3n = 21
.. n = 7
.. 2(7 -5) = d -5
.. 9 = d
The fraction is 7/9.