The recursive formula a2=18.5, an-1+1.5 models the number of people, in millions, that own a smartphone in the US, n years after 2014. Write an equivalent explicit formula for the situation.
By using arithmetic sequence, the equation explicit formula for the situation is \(a_{n}=1.5n-15.5\)
(\(n\geq 1\) and n is a whole number).
"Arithmetic sequences (arithmetic progressions) are ordered set of numbers that have a common difference between each consecutive term.
If we add or subtract the same number each time to make the sequence, it is an arithmetic sequence."
Given
It is an arithmetic sequence
\(a_{2}\) = 18.5, \(a_{n}= a_{n-1}+1.5\)
so, \(a_{1}= a_{2}-1.5\)
⇒\(a_{1}= 18.5-1.5\)
⇒\(a_{1}= 17\)
Common difference d = 1.5
Formula to find the equivalent explicit formula
\(a_{n}=a_{1}+(n-1)d\)
⇒\(a_{n}=17+(n-1)1.5\)
⇒\(a_{n}=17+1.5n-1.5\)
⇒\(a_{n}=1.5n-15.5\)
Hence, The equation explicit formula for the situation is \(a_{n}=1.5n-15.5\)
(\(n\geq 1\) and n is a whole number).
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