diketahui 3 suku pertama barisan aritmetika adalah (2x-7),(x+1),(3x-6). jumlah 12 suku pertama barisan tersebut adalah Tolong dijawab pake cara tolong bantuanny

a = U1 = 2x - 7
U2 = x + 1
U3 = 3x - 6

Beda Barisan
U2 - U1 = U3 - U2
(x + 1) - (2x - 7) = (3x - 6) - (x + 1)
- x + 8 = 2x - 7
2x + x = 8 + 7
3x = 15
x = 15/3
x = 5

U1 = 2x - 7 = 2 (5) - 7 = 10 - 7 = 3
U2 = x + 1 = 5 + 1 = 6
U3 = 3x - 6 = 3 (5) - 6 = 15 - 6 = 9

Beda Barisan
b = U2 - U1
b = 6 - 3
b = 3

Suku ke 12
U12 = a + 11b
U12 = 3 + 11 (3)
U12 = 3 + 33
U12 = 36

Jumlah 12 suku pertama
S12 = 1/2 n (a + U12)
S12 = 1/2 (12) (3 + 36)
S12 = 6 (39)
S12 = 234