Question

evaluate:
20
Σ(5k^2+3k)
k=1

Answer 1

can you simply plug in 20

Answer 2

i thought theres a formula u hav to use

Answer 3

n(n+1)/2

Answer 4

and n(n+1)(2n+1)/6

Answer 5

yes you are right, we can break this up into two sums. One will be sum form 1 to 20 of 5k^2 (here you can pull out the 5 as a constant and then simply use the formula you wrote above for the first n squares). Then the other summ will be the sum form 1 to 20 of 3k (again pull of the 3 as a constant). Then add the two values you get