#[http://mykhmsmathclass.blogspot.com/2011/09/formula-sum-of-first-n-terms-of-ap.html Formuladerivation ofsum of n termsof an AP] | #[http://mykhmsmathclass.blogspot.com/2011/09/formula-sum-of-first-n-terms-of-ap.html Formuladerivation ofsum of n termsof an AP] |