Question

Question #a4c2b

Answer 1

8

Explanation:

Original problem: `sum_(i=3)^11[1+(-1)^i]`

We can see that the value of `i` only changes the value of the `(-1)^i`. When `i` is odd, `1+(-1)^i=1+(-1)=0`. When `i` is even, `1+(-1)^i=1+1=2`.

Since the string of numbers for `i` is:
`{3,4,5,6,7,8,9,10,11}`
which has 5 odd values and 4 even values, therefore the sum is:
`5(0)+4(2)=8`

Answer: `8`