Answer: f(n) = 3.5n + 0.5
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Work Shown:
a = 4 is the first term
d = 3.5 is the common difference (we add this to each term to get the next term)
f(n) = nth term of arithmetic sequence
f(n) = a + d*(n-1)
f(n) = 4 + 3.5(n-1)
f(n) = 4 + 3.5n - 3.5
f(n) = 3.5n + 0.5
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As a check, we could plug in n = 1 to get
f(n) = 3.5n+0.5
f(1) = 3.5(1)+0.5
f(1) = 4
Showing that 4 is the first term. Now let's try n = 2
f(n) = 3.5n+0.5
f(2) = 3.5(2)+0.5
f(2) = 7.5
Which matches with the sequence also.
I'll let you confirm the other terms.