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Sn = 3n² – 4n

S1= 3 (1)² – 4(1) = 3-4= -1
S2= 3(2)² – 4(2) = 12-8 = 4

U2= S2- S1 = 4- (-1)= 5
b = u2- a = 5 – (-1) = 6

barisannya =  -1, 5, 11

u10 = a +9b = -1 + 9(6) = -1 + 54 = 53

Sn = 3n² – 4n
S1 = 3(1)² – 4(1)
S1 = 3 – 4
S1 = -1 (a = -1)

S2 = 3(2)² – 4(2)
S2 = 3(4) – 8
S2 = 12 - 8
S2 = 4

U2 = S2 – S1
U2 = 4 – (-1)
U2 = 4 + 1
U2 = 5
U2 = 5

b = U2 – U1/2 - 1
b = 5 – (-1) / 2 -1
b = 5 + 1 / 1
b = 6/1
b = 6

U10 = a + (n - 1)b
U10 = -1 + (10-1)6
U10 = -1 + 9 x 6
U10 = -1 + 54
U10 = 53