jumlah empat suku dan lima suku pertama baris aritmatika masing-masing 24 dan 35 suku ke 15 barisan tersebut adalah?

s4 = 1/2(4) [2a+ (4-1)b]
24 = 2[2a+3b]
24 = 4a+6b
s5 = 1/2(5) [2a+(5-1)b]
s5 = 5/2 [2a + 4b ]
35= 5a + 10b
dapat 2 persamaan
4a+6b = 24 Dikali 5
5a + 10b = 35 Dikali 4 hasil
20a+ 30b = 120
20a + 40b = 140 dikurangkan
-10b = -20
b = -20/-10 = 2
s4 = 1/2(4) [2a+ (4-1)b]
24 = 2 [2a + 3(2) ]
24 = 4a+12
4a = 24 - 12
a = 12/4 = 3

u 15 = a+14b
u15 = 3+14(2)
u15 = 3+28 = 31

semoga bisa membantu