nth term of a linear sequence (AP) = a+(n − 1)d first term = 6, last term = 10 sum − 40 i.e. a = 6, l = 10, S = 40 Sn= n/2(2a + (n − 1)d or Sn = ÷2 (a + l) Sn = n/2(a + l) 40 = n/2(6 + 10) 40 = 8n 8n = 40 8n = 40 n = 40/8 = 5 The number of terms = 5
