Determine if the following is always, sometimes, or never true.
y = -1/5 x + 3 is a function.

Question

Determine if the following is always, sometimes, or never true.
y = -1/5 x + 3 is a function.

anonymous · Answer

The given relation is a function if, when equal to y, the graph of the equation is intersected by a vertical line only once. See photo. $$y=\frac{ -x }{ 5 }+3$$ The above graph is always a function.

jhannybean · Answer

PERFECT EXPLANATION

loser66 · Answer

@Brenar can you give me the link of definition of function ?

anonymous · Answer

I'm sorry, can you clarify?

loser66 · Answer

It's new to me, I want to know base on which foundation, we can consider whether it 's a function or not

anonymous · Answer

http://en.wikipedia.org/wiki/Vertical_line_test

anonymous · Answer

Thank you very much! That explanation is great. :) @Brenar

loser66 · Answer

or just "cross" a vertical line?

jhannybean · Answer

@Loser66 http://tutorial.math.lamar.edu/Classes/Alg/FunctionDefn.aspx

jhannybean · Answer

Scrolldown to "working definition of a function"

loser66 · Answer

thanks

loser66 · Answer

@dan815 , dan when you online, answer my question here, please. I want to confirm the way we consider whether a relative is a function or not. I strongly agree with the helper above about it. My question is, there is some function doesn't work on that way, it's still a function but not onto or 1to 1. and it doesn't satisfy the vertical text above. For example: we discussed about the equation of the line x =4, now if I switch y =4, it doesn't pass the vertical test, it's a function still. I can rewrite y =4 under the form of a function f(x,4). Think about it and answer me, please. Obviously, if I ask you sketch the graph of f(x,4), you draw the line y =4. So???? Tell me what's wrong with my argument.

anonymous · Answer

If you clarify what you're asking a bit more, I can try to help you out.

loser66 · Answer

is f(x,4) a function?

anonymous · Answer

You can't have f(x,y). f(x) is saying that f is a function of x. You could have f(y) if your function was defined in terms of y, or vice versa.

loser66 · Answer

I don't think so, f(x, constant ) is an onto function, and it is a function of a horizontal line. My prof asked me define function of something like 
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