find the value for x if 12th term of the A.P. x-7, x-2, x+3...... is 81. find S12 also. Share with your friends Share 0 Varun.Rawat answered this Let a be the first term and d be the common difference.Now, a = x-7d = x-2-x-7 = x-2-x+7 = 5Now, a12 = 81⇒a + 11d = 81⇒x-7 + 11×5 = 81⇒x-7 + 55 = 81⇒x + 48 = 81⇒x = 33Now, sum of first n terms of an AP is given by :Sn = n22a+n-1d⇒S12 = 1222×26 + 11×5 = 652+55 = 642 3 View Full Answer