Integral mean value theorem

Let f:[a,b]R be Riemann integrable. Let

m:=infx[a,b]f(x),M:=supx[a,b]f(x).

Then there exists a number μ[m,M] such that

abf(x)dx=μ(ba).

If, in addition, f has the Darboux property (intermediate value property; for example if f is continuous or if f is a derivative), then there exists ξ[a,b] such that

abf(x)dx=f(ξ)(ba).