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The sum of the series 9 ,5,1,.to 100 terms is?
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The sum of the series 9 ,5,1,.to 100 terms is?
Calculating the Sum of an Arithmetic Series

An arithmetic series is a sequence of numbers with a constant difference between consecutive terms. The formula to calculate the sum of an arithmetic series is:

S_n = n/2 [2a + (n-1)d]

where S_n is the sum of the first n terms of the series, a is the first term, d is the common difference between terms, and n is the number of terms in the series.

Applying the Formula to the Given Series

In the given series, the first term (a) is 9, the common difference (d) is -4 (since each term is 4 less than the previous one), and the number of terms (n) is 100.

Substituting these values into the formula:

S_100 = 100/2 [2(9) + (100-1)(-4)]
S_100 = 50 [18 - 396]
S_100 = -18,900

Therefore, the sum of the series is -18,900.
Community Answer
The sum of the series 9 ,5,1,.to 100 terms is?
N = 100

a = 9

d = -4

so Sum = Sn = n / 2 *(a + an)

an = nth term = a+(n-1)d

= 9 + (100-1) (-4)

= 9 - 396

= -387

so Sum = 100/2 [9 + (-387)]

= 50 * (-378)

= - 18900
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The sum of the series 9 ,5,1,.to 100 terms is?
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