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Find S11 for 3 + 1 + (-1) + (-3) +… A. -77 B. -75 C. -73 D. -71
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Find S11 for 3 + 1 + (-1) + (-3) +… A. -77 B. -75 C. -73 D. -71

User Idm
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r=1-3=-2 \\ \\ a_(1)=3 \\ \\ n=11 \\ \\ S_(11)= (2*3+(11-1)*(-2))/(2) *11= (6-2*10)/(2)*11=-7*7=-77

\\\ Ben
User Bohdan Lyzanets
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