f(x+y)+f(x-y)=2f(x)Xf(y) f(x)定义在R上 求证 y=f(x)为偶函数拜托各位大神
问题描述:
f(x+y)+f(x-y)=2f(x)Xf(y) f(x)定义在R上 求证 y=f(x)为偶函数拜托各位大神
答
令y = 0时,则原函数化为f (x) + f (x) = 2 f (x)·f(0) 1.若f (x)=0时,则f (x)= f (-x)=0为偶函数 2.若f (x)≠0时,则f(0)=1 再令x = 0,则原式化为f (y)+ f (-y)=2 f (0) · f (y)=2 f (y) 即f (y) = f (-y),所以函数...