求证明;f(X)=f(x+1)+f(x-1)是周期函数

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求证明;f(X)=f(x+1)+f(x-1)是周期函数
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求证明;f(X)=f(x+1)+f(x-1)是周期函数
求证明;f(X)=f(x+1)+f(x-1)是周期函数

求证明;f(X)=f(x+1)+f(x-1)是周期函数
f(x + 1) = f(x) - f(x - 1)
f(x + 2) = f(x + 1) - f(x) = f(x) - f(x - 1) - f(x) = -f(x - 1)
f(x + 3) = f(x + 2) - f(x + 1) = -f(x - 1) - f(x) + f(x - 1) = -f(x)
f(x + 6) = f(x + 3 + 3) = -f(x + 3) = f(x)
所以f(x)是以6为周期的周期函数.

由题设可知,f(x) f(-x)=0.且f(-x)=f(x-1).===