#[http://mykhmsmathclass.blogspot.com/2011/09/sum-of-n-terms-of-ap-when-first-and.html Formula derivationsum of n termsof an AP whenfirst term andlast term is given] | #[http://mykhmsmathclass.blogspot.com/2011/09/sum-of-n-terms-of-ap-when-first-and.html Formula derivationsum of n termsof an AP whenfirst term andlast term is given] |