tolong ya !! saya udah nyoba tapi gak bisa ..

Sn = 2n² - 6n
S1 = 2(1²) – 6(1) = 2 – 6 = -4
S2 = 2(2²) – 6(2) = 8 – 12 = -4
S3 = 2(3²) – 6(3) = 18 – 18 = 0
Un = Sn – S(n-1)
U1 = S1 – S0 = -4 – 0 = -4
U2 = S2 – S1 = -4 – (-4) = 0
U3 = S3 – S2 = 0 – (-4) = 4
dst...
beda = U2 – U1 = 0 – (-4) = 4