Thursday, 14 December 2017

two real analysis problems on continuous functions




1.Let I=[a,b] and let f:IR be a continuous function on I such that for each x in I there exists y in I such that |f(y)|12|f(x)|.
Prove there exists a point c in I such that f(c)=0.
2.Let f be continuous on the interval [0,1] to R and such that f(0)=f(1). Prove that there exists a point c in [0,1/2] such that f(c)=f(c+1/2).






here are two problems on which I have completely stuck.can anyone guide me please to solve these problems


Answer



1) If |f(x)|>0 for all x[a,b] let x0 be the point where it attains its minimum. Can the stated condition hold at x0?



2) If f(0)=f(1/2) you are done. Otherwise consider g(x)=f(x)f(x+1/2). What can you say about g(0) and g(1/2)? Does g vanish somewhere in between?



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