How are we to understand the different uses of y in the equations y=0 and y=1/x? The lecture says that we should really use more variables. Can someone elaborate on how this work?

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anonymous · Answer

Could you be more specific or show link to the lecture? Thanks!

anonymous · Answer

If your talking about the part in the lecture I think your talking about, he is saying that we often drop the variable subscripts.  so, for instance, in the equation y=1/x, when we have y=0, this is really a bad example because it is undefined at y=0.

Lets say y=2x, though. and then you write y=0, your talking about a specific y for a specific x, to find the y-intercept. 

instead of going longhand and saying y(x)=2x. for what value of x will y(x) be zero, that specific y would have a subscript. instead you just write y=0 as if it were a general equation. similary, you may write x=0, which is an equation for a line, but you are only stating that x is equal to zero for a specific set of y(x) values. So it would normally and formally require a separate notation, which we drop for convenience.

make sense?