Tentukan jumlah 24 suku pertama dideret artimatika 3+7+11+ adalah

Diketahui       :  a = 3
                          b = U2 - U1 <=> 7 - 3 = 4
Ditanya          :  S24.......?
Penyelesaian : Sn = 1/2n [ 2a + ( n – 1 ) b ]
                          S24 = 1/2.24 [2.3 + (24-1) 4]
                          S24 = 12 [ 6 + (23) 4]
                          S24 = 12 [ 6 + 92]
                          S24 = 12 [ 98 ]
                          S24 = 1.176