1.

7 + 10 _ { 2 } ^ { 1 } + 14 + \ldots + 84

Answer»

first term (a)=7common difference=21/2-7=7/2Tn (nth term)=a+(n-1)d 84 =7+(n-1)7/2 84=7n/2 +7/2 24=n+1 n=23Sn=23/2 (7+84) = 23/2 (91) =1046.5



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