An=3 4n find the sum of 15 terms 149462-Find the sum of first 15 terms if an=3+4n

A 2 − a 1 = 11−7 = 4 a 3 − a 2 = 15−11 = 4 a 4 − a 3 = 19−15 = 4 Hence, a k 1 − a k is the same value every time Therefore, this is an AP with

Find the sum of first 15 terms if an=3+4n-=(34n) of an a p then the sum of the its 15 terms is Medium Solution Verified by Toppr First terms t 1 =34=7 15th term =34×15=63 ∴S 15 = 215 t 1 t 15 215 (763)=15×35=525 Was this answer helpful? Where, a = the first term l = the last term Putting n = 1 in the given an, we get a = 3 4 (1) = 3 4 = 7 For the last term (l), here n = 15 a15 = 3 4 (15) = 63 So, Sn = 15(7 63) 2 15 ( 7 63) 2 = 15 x 35 = 525 Therefore, the sum of the 15 terms of the given AP is S15 = 525