Question

Evaluate

Answer 1

i guess it is n=1 at the bottom ?

Answer 2

so you can split it into two terms :

sum of (-n-4) = sum of (-n) - 4*6 = - sumof (n) - 24

Answer 3

\[\sum_{n=1}^{6}(-n-4)\]

Answer 4

now there is formula for sum of first n terms ..

Answer 5

its n-1

Answer 6

so what is the first number of n or n-1

Answer 7

the sum goes from ? to 6

Answer 8

4 to 6

Answer 9

formula

Answer 10

I'm a bit confused now. What is this formula?

Answer 11

wait so the sum is from n-1=4 to 6 ?

Answer 12

yeah

Answer 13

so lets change the index
call n-1 = t
so the sum goes from
t=4 to t =6
and in the sum you have -t-5

Answer 14

so if you sum -5 three times you get -15

Answer 15

no as for the -t you have
- (4+5+6) = -15

Answer 16

-15-15 = -30

Answer 17

thanks

Answer 18

yw i hope i understood it correctly and it is fine