jumlah deret 3+6+9+...+117

Langsung aja y

Un = a + (n - 1)b
117 = 3 + (n - 1)3
117 = 3 + 3n - 3
3n = 117
n = 39

S39 = 39/2 (2a + 38b)
S39 = 19,5 (2.3 + 38.3)
S39 = 19,5 (6 + 114)
S39 = 19,5 × 120
S39 = 2.340

Semoga berguna +_+