I am doing the Khan Academy linear algebra course. I am around halfway through in which Sal talks about linear maps.
I am watching the video 'proof: Invertibility implies a unique solution to f(x)=y', in which he proves that for:
...there is only 1 unique $x$ that satisfies the equation.
He then says that because of this we can conclude that for:
...there is only 1 unique solution.
How does the first point imply the second? This is what has been stumping me.