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g(x)=f(h(x)), h is increasing

Source: ISI(BS) 2005 #6

June 23, 2012
functionlimitcalculusderivativealgebra proposedalgebra

Problem Statement

Let ff be a function defined on (0,)(0, \infty ) as follows: f(x)=x+1xf(x)=x+\frac1x Let hh be a function defined for all x(0,1)x \in (0,1) as h(x)=x4(1x)6h(x)=\frac{x^4}{(1-x)^6} Suppose that g(x)=f(h(x))g(x)=f(h(x)) for all x(0,1)x \in (0,1).
(a) Show that hh is a strictly increasing function.
(b) Show that there exists a real number x0(0,1)x_0 \in (0,1) such that gg is strictly decreasing in the interval (0,x0](0,x_0] and strictly increasing in the interval [x0,1)[x_0,1).