diketahui tiga suku pertama barisan aritmatika adalah(2x+1),(x+2)dan(2x-3). suku ke 15 barisan tersebut adalah???

B = b
U2 - U1 = U3 - U2
x + 2 - (2x + 1) = 2x - 3 - (x + 2)
x + 2 - 2x - 1 = 2x - 3 - x - 2
-x + 1 = x - 5
1 + 5 = x + x
6 = 2x
x = 6 : 2
x = 3

U1:
2x + 1 = 2 × 3 + 1
2x + 1 = 6 + 1
2x + 1 = 7

U2:
x + 2 = 3 + 2
x + 2 = 5

U3:
2x - 3 = 2 × 3 - 3
2x - 3 = 6 - 3
2x - 3 = 3

b = U2 - U1
b = 5 - 7
b = -2

U15 = a + (n - 1) . b
U15 = 7 + (15 - 1) . (-2)
U15 = 7 + 14 . (-2)
U15 = 7 - 28
U15 = -21