I've been stuck on this worksheet for days now.. we're working on derivatives now and my teacher gave us a few word problems and for most of them i think i got the correct function but am a bit doubtful when it come to my abilities (especially after my teacher told my friend behind my back that i was not reliable source

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Anyways, the first of the equations should be easy i know but i just want to check on it. Question: Find the point(s) on the graph of y= 4 - x^2 that is closest to the point(0,2)

For this one i know that we use the distance formula and the domain is all real numbers, but im not quite sure how to replace the "y" in the equation for x so that there would be only one variable.