Precalculus
posted by Laura .
Find the sum of 20 (summation notation symbol)k=1 then (3k5)
If you mean the sum of the first 20 terms, beginning with k=1, of
ak = 3k  5,
that would be 20 x 5 = 100
PLUS the sum of the first 20 terms of
ak = 3k
The latter is 3 times the sum of
1+2+3+...20 ,
or 3*(20)(21)/2= 630
So the answer is 630  100 = 530
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