#how to prove that f is constant ?

33 messages · Page 1 of 1 (latest)

buoyant kiln
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f is a continuous function in [0,1] in which if x is in [0,1] f(x/2) + f((x+1)/2) = 2f(x) , i have already managed to prove that f is bounded and f(0) = m the maximum of the function, but i'm totally stuck for the second question asking us to show that f is constant, my idea was to show the fact that f(0) = m => f(x) = m for any x we chose in [0,1] by combining "/2" "(...+1)/2" operations but i don't know how to do write it properly

clever trenchBOT
sinful mural
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also no info on domain?

buoyant kiln
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yes the function is defined and continuous in [0,1] and take values in R

sinful mural
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so

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we know that if x = 1 then f(1/2)+f(1)=2f(1)

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idk if that helps

buoyant kiln
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so that means we would have f(1/2) = f(1) ?

sinful mural
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when x=1 yeah

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and you know it is continuous on 1

sinful mural
buoyant kiln
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why is it true for any x in [0,1] and not just 1 ?

sinful mural
buoyant kiln
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yes

sinful mural
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and you got the max on f(0)

buoyant kiln
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yes

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i feel so dumb i'm sorry 😭

sinful mural
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you arent dumb

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you got the max in [0,1]

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?

buoyant kiln
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we have the max m in [0,1] and f(0) = m

sinful mural
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yeah

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and f(1/2) = m

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put x = 1/2

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Have you learned dyadic rationals

buoyant kiln
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yes we have f(1/2) = m f(1) = m but how to show that it equals m for any x

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no but it is like a density thing ? because we learned density

sinful mural
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they are dense in [0,1]

buoyant kiln
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ooooooooooo

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so if we show that every for every diadic rationnal n we have f(n) = m then we prove that f is constant

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wait tysm i think i have found something

sinful mural
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good luck then