Help Solve Math Homework Qs -3, -1, 1 & CD 2

[Skaterkid]

Homework Statement

http://puu.sh/ajGv

Homework Equations

??

The Attempt at a Solution

Q1- is -3, -1 and 1
Q2- CD is 2
Q3- I don't understand hence can't even start it

 

[Mentallic]

That expression just means what is the sum of 2r-5 from r=1 up to n. So, what is

(2(1)-5)+(2(2)-5)+(2(3)-5)+...+(2(n)-5)

You should have been given a formula to calculate the sum of an arithmetic series.

 

[mtayab1994]

use the following:

 

[mtayab1994]

Did you reach your answer yet?