- #1
Scienticious
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Homework Statement
Show that if f: A → B and E, F are subsets of A, then f(E ∪ F) = f(E) ∪ f(F).
Homework Equations
The Attempt at a Solution
My attempt:
Suppose x is an element of E. Then f(x) is an element of f(E), which means f(x) is a subset of f(E).
But x is in E implies x is in E or F so that x is in E ∪ F.
Thus f(E ∪ F) = f(x) is a subset of f(E), and is also a subset of f(E) ∪ f(F) by or introduction.
*Similar argument applies when we suppose x is an element of F*
Now I'm having trouble with the converse part of the proof; the only idea I've come up with is to use a similar strategy as in the first proof and suppose x is in E so that f(x) is in f(E). Then you can show that since x is in E or F that the left side of the equation is contained in the right.
I'm a total newbie at proofs. please someone help me out :3