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Question Number 213564 by tri26112004 last updated on 09/Nov/24

f: Z→R such that  f(x).f(y)=f(x+y)+f(x−y)  ⇒f(x)=¿

f:ZRsuchthatf(x).f(y)=f(x+y)+f(xy)f(x)=¿

Commented by mr W last updated on 09/Nov/24

f(x)=2 cos x

f(x)=2cosx

Commented by tri26112004 last updated on 09/Nov/24

your solution¿

yoursolution¿

Commented by mr W last updated on 09/Nov/24

i don′t know if there are other   solutions.

idontknowifthereareothersolutions.

Commented by Ghisom last updated on 09/Nov/24

I think f(x) can be any function with  f(0)=2∧f(x)=f(−x)

Ithinkf(x)canbeanyfunctionwithf(0)=2f(x)=f(x)

Commented by mr W last updated on 09/Nov/24

if you were right, then f(x)=2+x^2   is also a solution. but it isn′t!

ifyouwereright,thenf(x)=2+x2isalsoasolution.butitisnt!

Commented by Ghisom last updated on 10/Nov/24

you′re right

youreright

Answered by issac last updated on 09/Nov/24

weyl−wigner transform  Φ[f(u,v)]=(1/(4π^2 ))∫∫_(S∈R^2 )   dudv f(u,v)e^(iuQ+ivP)   set R=(−∞,∞)  and double integrals interval  R^2  mean X×Y=(−∞,∞)×(−∞∞)

weylwignertransformΦ[f(u,v)]=14π2SR2dudvf(u,v)eiuQ+ivPsetR=(,)anddoubleintegralsintervalR2meanX×Y=(,)×()

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