Find the sum of the series:

I do the sum and each time I get a different answers, none of them matching with the answer in my book.

Book's answer:-n(2n+1)

My latest answer: -3n(2n-1)

My latest working:

(a)

starting from r=1, there is (n-1) terms and 1^2 have to be added separately.

(b)

starting from r=1, there is n terms.

----

(a)

(b)

Summation=(a)-(b)=-6n^2+3n

=-3n(2n-1)

Can you please narrow down the field where I should search the error?

I am exasperated looking through my rough handwriting.