berapa jumbah suku yang ke 100 dari barisan 3,7,11,15

A = 3
B = 7-3 = 4

S100 :
= n/2 [2a + (n-1) x b]
= 100/2 [2 x 3 + (100-1) x 4]
= 50 [6 + 99 x 4]
= 50 [6 + 396]
= 50 x 402
= 20.100

Mapel : Matematika
Kelas : IX SMP
Bab : Barisan dan deret

Pembahasan :
Un = a + (n - 1)b
U100 = 3 + (n - 1)4
U100 = 3 + 4n - 4
U100 = 4n - 1
U100 = 4(100) - 1
U100 = 399

Maka...
Sn = n/2(a + Un)
S100 = 100/2(a + U100)
S100 = 50(3 + 399)
S100 = 50(402)
S100 = 20.100