I expanded the functions in the taylor and got

y(x+h) = y(x) + hy'(x) + h^2/2*y"(x) + h^3/6y"'(x) + h^4/12*O(h^4)

y(x+h) = y(x) - hy'(x) + h^2/2*y"(x) - h^3/6y"'(x) + h^4/12*O(h^4)

y(x+2h) = y(x) + 2hy'(x) + h^2*y"(x) + h^3/3y"'(x) + h^4/6*O(h^4)

y(x+2h) = y(x) - 2hy'(x) + h^2*y"(x) - h^3/3y"'(x) + h^4/6*O(h^4)

im not sure if i went too far or what. please help