Verifying the Sum of an Arithmetic Progression: Is it -(p+q) or +(p+q)?

[phymatter]

my book says that if sum of p terms of an ARTHMETRIC PROGRESSION is q and sum of q terms is p , then sum of p+q terms will be -(p+q) , but i am getting it as +(p+q),
can someone verify it ?

 

[jav]

Can you post your work?

Just messed around with it for a couple minutes and I got p+q+p*q*d where d is the common difference.