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What is the sum of the first 11 terms of the arithmetic series in which a1= -12 and d=5?
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What is the sum of the first 11 terms of the arithmetic series in which a1= -12 and d=5?

User Imad Ullah
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1 Answer

3 votes
Hello :
the terme general is : an = a1 +(n-1)d
a11 = a1+(11-1)×5
a11 = -12+50
a11 = 38
the sum of the first 11 terms is : S11 = (11/2)(a1+a11)
S11 = (11/2)(-12+38)
S11 = 143
User Bludzee
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