抽象函数证明f(x+y)+f(x-y)=2f(x)f(y) f(1)≠0证明为偶函数
3个回答
先令y=0,则有2f(x)=2f(x)f(0)
则有f(0)=1
再令x=0,则有f(y)+f(-y)=2f(0)f(y)
则有f(-y)=f(y),为偶函数,得证
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