provided all terms in the expression are well defined is a second order finite difference scheme for second order derivative.
I know how to approach this question. I know I use the taylor expression and everything but I don't know which formula to use. For example, I know that when finding a first order derivative I use
I've already solved a question using this but I don't know what the formula is for $u''(x)$.
Would it be something like
$u''(x)=au(x+3h)+bu(x+2h)+cu(x+h)+du(x)+eu(x-3h)+fu(x-2h)+g(x-h) ? $
I'm pretty sure this is wrong because I don't think I should have this many unknowns. What equation should I be using?