Proving AUB & A∩B Inverse Functions of g

[mtayab1994]

Homework Statement

Let g be a function from ℝ to ℝ and for all subsets A and B of R.

Homework Equations

Prove that:
g^{-1}(A\cup B)=g^{-1}(A)\cap g^{-1}(B)
and
g^{-1}(A\cap B)=g^{-1}(A)\cup g^{-1}(B)

The Attempt at a Solution

Our teacher gave us this problem but I think it's wrong because I was easily able to prove that:
g^{-1}(A\cup B)=g^{-1}(A)\cup g^{-1}(B)
and
g^{-1}(A\cap B)=g^{-1}(A)\cap g^{-1}(B)
but when i try to solve what he gave us this is all I can do:

x\in g^{-1}(A\cup B)\Longleftrightarrow g(x)\in A\cup B\Longleftrightarrow g(x)\in Aorg(x)\in B\Longleftrightarrow x\in g^{-1}(A)\cup g^{-1}(B)

and the same goes for the second one. Can anyone tell me where I'm going wrong?

 

[pasmith]

Homework Statement

Let g be a function from ℝ to ℝ and for all subsets A and B of R.

Homework Equations

Prove that:
g^{-1}(A\cup B)=g^{-1}(A)\cap g^{-1}(B)
and
g^{-1}(A\cap B)=g^{-1}(A)\cup g^{-1}(B)

These are wrong. A counterexample to both is the zero function g(x) \equiv 0 with A = \{0\} and B = \{1\}.

The Attempt at a Solution

Our teacher gave us this problem but I think it's wrong because I was easily able to prove that:
g^{-1}(A\cup B)=g^{-1}(A)\cup g^{-1}(B)
and
g^{-1}(A\cap B)=g^{-1}(A)\cap g^{-1}(B)

These are correct.