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  • Brainly User
2015-09-05T17:04:10+08:00

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Arithmetic sequence:

an = a1 + (n-1)(d)

an = is the term
a1 = the first term
n = the  order of the term in the given series
d = common difference (difference between the consecutive sequence must be the same

Given:
a9 = ?
a1 = 10
n = 9 (9th term)
d =  -1/2

a9 = 10 + (9-1) (-1/2)
a9 = 10 + (8) (-1/2)
a9 = 10 + (-4)
a9 = 6

The 9th term is 6.
If the common difference is negative (-), the sequence is in decreasing order:
In this sequence, -1/2 = -0.5
    10, 9.5, 9, 8.5, 8, 7.5, 7, 6.5, 6, ...

 

0
2015-09-05T18:47:55+08:00
A9=a1 + (n-1)d
A9=10 + (8)-1/2
A9=10 + -4
A9=6
0