Saturday, 30 July 2016

real analysis - Proving that the function is bounded by the function of its derivative on the given interval

Suppose h:RR is differentiable everywhere and h is continuous on [0,1], h(0)=2 and h(1)=1. Show that:

|h(x)|max(|h(t)|,t[0,1]) for all x[0,1]



I attempted the problem the following way:

Since h(x) is differentiable everywhere then it is also continuous everywhere. h(0)=2 and h(1)=1 imply that h(x) should cross x-axis at some point (at least once). Denote that point by c to get h(c)=0 for some c[0,1].

h(x) continuous means that lim[h(x)]=h(a) as xa but then I am stuck and I don't see how what I have done so far can help me to obtain the desired inequality.

Thank you in advance!

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