AP - general term

Find the sum of the first 12 terms of the arithmetic sequence whose general term is an=3n+5.

Correct answer:

s12 =  294

Step-by-step explanation:

a1=3 1+5=8 a2=3 2+5=11 a3=3 3+5=14 n=12  d=a2a1=118=3  a12=a1+(n1) d=8+(121) 3=41  s12=n 2a1+a12=12 28+41=294

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