Diketahui barisan aritmetika s4=,15Dan s12=47 tentukan: A.s1 Dan beda B.rumus suku1 me-n,Dan C.s1,s2,s3,s4,s5

S4 = a + 3b = 15
S12 = a + 11b = 47
-------------------------- (-)
8b = 32
b = 32/8
b = 4

a + 3b = 15
a + 3(4) = 15
a + 12 = 15
a = 15 - 12
a = 3

Un = a + (n - 1)b
Un = 3 + (n - 1)4
Un = 3 + 4n - 4
Un = 4n - 1

S2 = 2/2 ( 2a + b )
S2 = (2(3) + 4 )
S2 = 6 + 4
S2 = 10

S3 = 3/2 ( 2a + 2b )
S3 = 3/2 . 2 ( 3 + 4)
S3 = 3 (7)
S3 = 21

Sn = n/2 ( 2a + (n - 1)b)
Sn = n/2 ( 2(3) + 4n - 4)
Sn = n/2 ( 4n + 2 )
Sn = n/2 . 2(2n + 1)
Sn = n ( 2n + 1)