Rumus suku ke N dan jumlah 20 suku pertama pada barisan 10,15,20,25,30,.......

A = 10
B = 15-10 = 5

Un :
= a + (n-1) x b
= 10 + (n-1) x 5
= 10 + 5n -5
= -5 + 5n

S20 :
= n/2 [2a + (n-1) x b]
= 20/2 [2 x 10 +(20-1) x 5]
= 10 [20 + 19 x 5]
= 10 [20 + 95]
= 10 x 115
= 1150

Barisan aritmatika
a = 10
b = 5

Un = a + (n-1)b
Un = 10 + (n-1)5
Un = 10 + 5n - 5
Un = 5 + 5n

S20 = n/2(2a+(n-1)b)
S20 = 20/2(2.10+(20-1)5)
S20 = 10(20+(19)5)
S20 = 10(20+95)
S20 = 10(115)
S20 = 1150

#CMIIW