(r^{th}) term (=3r+1)
[ S_{20}=\sum_{r=1}^{20}(3r+1)=3\cdot\dfrac{20\cdot21}{2}+20=630+20=650 ]
Answer: (650)
11TH•Mathematics•Sequences And Series•Question 7
Overview
Find the sum of 20 terms of the series whose $r^{th}$ term is $3r + 1$.
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