function trapquad(f,a,b,n)
	h=(b-a)/n
	x(k)=a+k*h
	return sum((f(x(k-1))+f(x(k)))/2*h for k=1:n)
end

A=5*log(5)-4
E(n)=abs(trapquad(log,1.0,5.0,n)-A)

ns=2.0.^(1:16)
hs=(5-1)./ns
Es=E.(ns)

using Plots
scatter(hs,Es,xscale=:log10,yscale=:log10,legend=false)
plot!(h->h^2,hs)