Find the sum of arithmetic sequence -8,-5,-2, _______, 7?
- 5
- 8
- -3
- -8
Explanation
Given sequence: -8, -5, -2, ..., 7
We have:
a = -8 (first term)
d = 3 (common difference)
Let 7 be the nth term
Using the formula: tn = a + (n - 1) d
7 = -8 + (n - 1) 3
Solving for n:
15 ÷ 3 = n - 1
n = 6
Now we have:
a = -8
d = 3
n = 6
Substituting these values in the formula for sum:
S₆ = (6/2) × [2 × (-8) + (6 - 1) × 3]
= (6/2) × [-16 + 15]
= 3 × -1
= -3
Therefore, the sum of the given sequence is -3.
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