1.2, 3, 7.5, 18.75, ...

Which formula can be used to describe the sequence?

f(x) = 1.2(2.5)x – 1
f(x) = 2.5(1.2)x – 1
f(x) = 1.2(2.5)x
f(x) = 2.5(1.2)x

a(n) = 1.2*(5/2)^(n - 1)

Step-by-step explanation:

The fast growth of this sequence suggests that it's a geometric sequence, not an arithmetic one.

Dividing 3 by the first term, 1.2, yields 5/2.  Multiplying the second term, 3, by 5/2 yields 7.5, which agrees with the given sequence.  Thus, we have found and confirmed the common ratio:  It is 5/2, and the first term is 1.2.

Thus, the explicit formula for this ratio is

a(n) = 1.2*(5/2)^(n - 1)

This is equivalent to answer choice f(x) = 1.2(5/2)x – 1.  Note that you MUST enclose your  " x - 1 " in parentheses here, obtaining:

f(x) = 1.2(5/2)^(x – 1).  The exponentiation symbol " ^ " is also mandatory.

"f(x) = 1.2(2.5)x-1"

Step-by-step explanation:

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