Question

Hasil dari 17+20+23+...+80 adalah ......

Answer 1

U1 = 17
b = u2 - u1
   = 20 - 17
   = 3
s80 = n/2 (2a + (n - 1) b)
      = 80/2 (2 x 17 + (80 - 1)3)
      = 40 (34 + (79 x 3)
      = 40 (34 + 237)
      = 40 (271)
      = 10840

Answer 2

Sn = n/2 . (2a + (n-1).b)
b(beda) = 20-17 = 3
Un = a+ (n-1). b
80(suku terakhir) = 17 + (n-1) . 3 
80 = 17 + (n-1) . 3
80 = 17 + 3n - 3
80 = 14 + 3n
66 = 3n
n = 22
Sn= n/2 . (2a + (n-1) . b)
Sn = 22/2 . (2.17 + (22-1) . 3)
Sn = 11 . (34 + 21 . 3)
Sn = 11.  (34 + 63)
Sn = 11.97
Sn = 1067