Parabolic sequence

Find the sum of the first nine terms of an arithmetic sequence whose general term is a(n) = 3n2+5

Correct answer:

s =  900

Step-by-step explanation:

a1=3 12+5=8 a2=3 22+5=17 a3=3 32+5=32 a4=3 42+5=53 a5=3 52+5=80 a6=3 62+5=113 a7=3 72+5=152 a8=3 82+5=197 a9=3 92+5=248  s=a1+a2+a3+a4+a5+a6+a7+a8+a9=8+17+32+53+80+113+152+197+248=900

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