Dik barisan aritmatika U3=18 dan U7=38,tentukan 30 suku pertama(pake jalan)

[tex]u7 = a + 6b = 38[/tex]
[tex]u3 = a + 2b = 18[/tex]
lalu di kurang
[tex] = 4b = 20[/tex]
b = 5

lalu pakai cara subsitusi
U3= a+ 2b
18 = a + 2(5)
18= a+ 10
a= 8

jadi suku 1/a/U1 = 8

U3 = 18
U7 = 38


U3 = a+2b = 18
U7 = a+6b = 38
____________-
-4b = -20
b=5

U3 = a+2b
18 = a +2(5)
18 = a + 10
a = 8

S30 = n/2 ( 2a+(n-1)b)
= 15 (2.8+29.5)
= 15 (16+145)
=15.161
= 2.415