(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Let f: X[tex]\rightarrow[/tex]Y and g: Y[tex]\rightarrow[/tex]Z be functions. Prove or disprove the following: if g[tex]\circ[/tex]f is onto and g is one-to-one then f is onto.

2. Relevant equations

N/A

3. The attempt at a solution

I'm honestly not sure what to do with this. I believe that the statement is true as I cannot think of an instance where it would be false, however actually proving it is another story. I know that:

since g[tex]\circ[/tex]f is onto that [tex]\forall[/tex]z[tex]\in[/tex]Z, [tex]\exists[/tex]x[tex]\in[/tex]X so that g[tex]\circ[/tex]f(x) = z

and I believe g must be onto so [tex]\forall[/tex]z[tex]\in[/tex]Z, [tex]\exists[/tex]y[tex]\in[/tex]Y so that g(y) = z.

and since g is one-to-one [tex]\forall[/tex]y,z[tex]\in[/tex]Y, if g(y) = g(z) then y=z.

I just don't know what to do with all of that. I've started by assuming y[tex]\in[/tex]Y and x[tex]\in[/tex]X but again I don't know what to do with those assumptions =\.

Since I believe the statement true I want to show [tex]\forall[/tex]y[tex]\in[/tex]Y, [tex]\exists[/tex]x[tex]\in[/tex]X si tgat f(x)=y.

Anyway I've been mashing my head against a wall over this to no avail so far. If anyone could help me I'd greatly appriciate it. This is for an assignment that's due tomorrow and it's the last one I'm unable to get. FYI the reason I said g is onto is from a previous question I had to show if g[tex]\circ[/tex]f is onto then g must be onto as well.

Oh, and sorry for the horrible formatting, I'm not to good with the formula creator.

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# Homework Help: Onto composite function

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