Question
Find the sum of 20 (summation notation symbol)k=1 then (3k-5)
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
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