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Write the explicit formula for the arithmetic sequence.

3, -3, -9, -15, -21, ...
A) an = 7 - 4n
B) an = 6 - 3n
C) an = 9 - 6n
D) an = 18 - 15n

User Yagiro
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Option C

The explicit formula for the arithmetic sequence is
a_n = 9 - 6n

Solution:

Given that the arithmetic sequence is:

3, -3, -9, -15, -21, ...

To find: Explicit formula for the arithmetic sequence

The nth term of an arithmetic sequence is given by:


a_n = a_1 + (n - 1)d

Where
a_n is nth term of sequence

n is the term's location


a_1 is the first term of sequence

d is the common difference between terms

In an arithmetic sequence, the difference between successive terms is constant. This means that we can move from any term to the next one by adding a constant value.

In the given sequence:

3, -3, -9, -15, -21, ...


a_1 = \text{ first term } = 3

d = difference between any two terms in sequence


d = a_2 - a_1

d = -3 - (3) = -6

Substituting the values in above formula,


a_n = 3 + (n - 1)(-6)\\\\a_n = 3 -6n + 6\\\\a_n = 9 - 6n

Thus the explicit formula to find any term in sequence is found

User Nyuen
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