Indicate the general rule for the arithmetic sequence with a3 = -12 and a8 = -37.
Solution:
A sequence where the difference between each successive pair of terms is the same is called an arithmetic sequence.
The general rule of arithmetic sequence is
an = a1 + (n - 1)d
Where a1 - first term
n - number of terms
It is given that
a3 = -12 and
a8 = -37
If a3 = -12 using the arithmetic sequence rule we get
a + (3 - 1) d = -12
a + 2d = -12
We can write it as
a = - 12 - 2d …. (1)
If a8 = -37 using the arithmetic sequence rule we get
a + (8 - 1) d = -37
a + 7d = -37 ….. (2)
Let us substitute equation (1) in (2)
- 12 - 2d + 7d = -37
- 12 + 5d = -37
5d = - 37 + 12
5d = -25
Dividing both sides by 5
d = - 5
Substituting the value of d in equation (1)
a = -12 - 2 (-5)
a = -12 + 10
a = - 2
Therefore, the general rule for the arithmetic sequence is an = - 2 + (n - 1) (-5).
Indicate the general rule for the arithmetic sequence with a3 = -12 and a8 = -37.
Summary:
The general rule for the arithmetic sequence with a3 = -12 and a8 = -37 is an = - 2 + (n - 1) (-5).
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