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5 votes
Please help!
10
∑ 2i-9
i=3

1 Answer

2 votes


\sum\limits_(i=3)^(10)(2i-9)=2(3)-9+2(4)-9+2(5)-9+2(6)-9+2(7)-9\\\\+2(8)-9+2(9)-9+2(10)-9\\\\=6-9+8-9+10-9+12-9+14-9+16-9+18-9+20-9\\\\=90-72=18

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