Answer: Choice C
18+7(n-3)
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Step-by-step explanation:
We can rewrite the right hand side of choice C like so
18+7(n-3)
18+7(n-1-2)
18+7(n-1)+7(-2)
18+7(n-1)-14
4+7(n-1)
Which is now in the form a+d(n-1)
- a = 4 = first term
- d = 7 = common difference
This confirms choice C to be arithmetic. The other choices cannot be written in the format of a+d(n-1). Choices A and B are quadratic sequences while choice D is exponential.
The first few terms of choice C are: 4, 11, 18, 25, 32, ...
To get new terms, add 7 to the previous one.
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Notice how if n = 5 for instance, then,

and

This confirms that
when n = 5. I'll let you check other positive integer values for n.