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Find the sum of the first 20 terms of the arithmetic sequence -11, -3, 5, 13, ...

 Jul 25, 2020
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common differece, d = 8         a1 = 11        a20 = -11 + 8(19) = 141

 

Sum = n/2 (a1 + a20)

        = 20/2 (-11 + 141) = ..........

 Jul 25, 2020

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