4+9+14+19 tentukan jumlah tiga puluh suku pertama

a = 4

b= u2-u1 = 9-4 = 5

S30= n/2 (2a+(n-1)b)

S30 = 30/2 (2.4 + (30-1).5)

S30 = 15 (8 + (29.5))

S30 = 15 . (8 + 145)

S30 = 15 . 153

S30 = 2295