SOLUTION: What is the sum of the first 45 terms of the following sequence? 20, 18, 16, . . .

Question 757230: What is the sum of the first 45 terms of the following sequence?
20, 18, 16, . . .
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
What is the sum of the first 45 terms of the following sequence?
20, 18, 16, . . .
----
a = 20
d = -2
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S(n) = (n/2)(a+a(n))
----
a(n) = a + (n-1)d
a(45) = 20 + 44*-2 = 20-88 = -68
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S(45) = (45/2)(20 - 68)
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= 22.5(-48)
---
= -1080
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Cheers,
Stan H.
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