[線代] 證明是否是子空間

[dondonmike (我很單純)]

Let V be the real vector space of all function f from R to R
prove or disprove following sets of functions are subspace of V

1. all f such that f(x^2)=f(x)^2
2. all f such that f(0)=1
3. all f such that f(0)=1+f(1)
4. all f which are continues

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→ dondonmike  :ok，我懂這兩個東西可是怎麼證明？
推 LoveBeef5566:f[(x+y)^2]≠f(x)^2+f(y)^2
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