suatu deret aritmatika suku ke-3 dan ke-5 berturut turut 10 dan 16. berapakah jumlah suku ke-9

Bab Pola Bilangan

U3 = a+(3-1)b
a+2b = 10

U5 = a+(5-1)b
a+4b = 16

a + 4b = 16
a + 2b = 10
__________ -
2b = 6
b = 6/2
b = 3

a + 2b = 10
a + 2(3) = 10
a + 6 = 10
a = 10 - 6
a = 4

Sn = n/2 (2a + (n-1)b)
S9 = 9/2 (2×4 + (9-1)3)
S9 = 9/2 (8 + 24)
S9 = 9/2 (32)
S9 = 9(16)
S9 = 144

gunakan metode eliminasi
U3 = a + 2b = 10
U5 = a + 4b = 16
____________-
-2b = -6
b = 3

gunakan metode subtitusi
a + 2b = 10
a + 2(3) = 10
a = 10 - 6
a = 4

maka

Sn = n/2 (2a + (n-1)b)
S9 = 9/2 (2(4) + (9-1)3)
S9 = 4,5 (8 + 24)
S9 = 4,5 (32)
S9 = 144

semoga berguna +_+