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Question

Let fx=11-x. Then, f o fof x
(a) x for all x R
(b) x for all x R-1
(c) x for all x R-0, 1
(d) none of these

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Solution

Domain of f:1-x0x1Domain of f=R-1Range of f:y=11-x1-x=1yx=1-1yx=y-1yy0Range of f=R-0So, f:R-1R-0 and f:R-1R-0 Range of f is not a subset of the domain of f.Domain fof=x: xdomain of f and fxdomain of fDomain fof=x: xR-1 and 11-xR-1 Domain fof=x: x 1 and 11-x1Domain fof=x: x 1 and 1-x1Domain fof=x: x 1 and x0Domain fof=R-0, 1fofx=ffx=f11-x=11-11-x=1-x1-x-1=1-x-x=x-1xFor range of fof, x0Now, fof:R-0, 1R -0 and f:R-1R-0Range of fof is not a subset of domain of f.Domainf o fof=x: xdomain of fof and fofxdomain of fDomain f o fof=x: xR-0, 1 and x-1xR-1 Domainf o fof=x: x 0, 1 and x-1x1Domain f o fof=x: x 0, 1 and x-1xDomain f o fof=x: x 0, 1 and xRDomain f o fof=R-0, 1fofofx=ffofx=fx-1x=11-x-1x=xx-x+1=xSo, fofofx=x, where x0,1
So, the answer is (c).

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