Use error bound ET=−(b−a)312n2f′′(ξ)E_T = -\frac{(b-a)^3}{12n^2} f''(\xi)ET=−12n2(b−a)3f′′(ξ) for some ξ∈(a,b)\xi \in (a,b)ξ∈(a,b).
