rumus suku ke n dari barisan bilangan -2,-2,0,4 adalah

a+b+c = -2
3a+b = 2
2a = 1

=> 2a = 1
a = 1/2
=> 3a + b = 2
3(1/2)+b = 2
b = 2 - 3/2
b = 1/2

=>a + b + c = -2
1/2 + 1/2 + c = -2
c = -2 -1
c = -3

Un = an^2 + bn + c
= 1/2n^2 + 1/2n - 3
= 1/2n (n +1) - 3