numerical

Suppose that ϕ(h) is an approximation to some quantity M for every h > 0

and that

M = ϕ(h) + a2h^2 + a4h^4+ a6h^6 + . . .

for some constants a2, a4, a6, . . . Use the values ϕ(h), ϕ(h/

3 ) and ϕ(h/

9 ) to produce an O(h^6)

approximation to M.