推 onechina :let f=0 for all x in R, try A={0} and B={1,0} 09/28 17:36
→ pig60912002 :上面是A包含於X與B包含於Y~ 09/28 19:59
Suppose that f:X →Y with A⊆X and B⊆Y. Find examples which show that the
given equalities are false.
(1)f-1(f(A))=A
(2)f(f-1(B))=B
※f-1為反函數
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