0 12 10 0 -12 -20
I calculate the differences, and find it's a 3rd degree polynomial.
So I know when n=1 the above equation=0, and when n=2, 12, and so on.
So I come up with these 4 equations
a + b+ c+d=0
Now I have to solve this system of linear equations. I just keep trying and getting wrong answers. What's the best way to attack this problem?