dari barisan aritmetika diketahui 1suku ke-3 = 14 dan suku ke-7 = 26. jumlah 18 suku pertama adalah...

Mapel : Matematika
Bab : Barisan dan deret

U3 = a + 2b = 14
U7 = a + 6b = 26
_____________ _
-4b = -12
b = 3

a + 2b = 14
a + 2(3) = 14
a + 6 = 14
a = 8

S18 = 18/2(2(8) + (18 - 1)3)
S18 = 9(16 + 51)
S18 = 9(67)
S18 = 603

u3 = a + 2b = 14 -
u7 = a + 6b = 26
-4b = -12
b = -12/-4 = 3

a + 2b = 14
a + 2.3 = 14
a = 14 - 6
a = 8

s18 = 18/2 (2.8 + (18-1)3)
s18= 9 (67)
s18 = 603