# function help?

• Nov 27th 2013, 06:57 AM
eliT
function help?
I have a question, and would appreciate help in answering it. Thank you.

"show that y^2 - xy - 2 = 0 cannot be a function ƒ(x) for x ∈ R."
• Nov 27th 2013, 08:24 AM
Plato
Re: function help?
Quote:

Originally Posted by eliT
I have a question, and would appreciate help in answering it. Thank you.
"show that y^2 - xy - 2 = 0 cannot be a function ƒ(x) for x ∈ R."

Suppose that $\displaystyle \mathcal{G}=\{(x,y): y^2-xy-2=0\}$ is the graph.

Is it true that $\displaystyle (1,-1)\in \mathcal{G}~\&~(1,2)\in \mathcal{G}~?$

What does that tell you?
• Nov 27th 2013, 09:19 AM
eliT
Re: function help?
I am so sorry, but I don't know what any of that is. I've spent hours trying to understand. I've done tons of questions (correctly) but I just don't know what to write as the answer to this question. I was seriously hoping someone could tell me what equation or statement actually answers the question that was asked. But so far on three different forums the only replies I get are people asking me questions, giving vague hints I don't understand or telling me to research functions. I'm fairly close to tears now... so tired of trying and only failing to understand.
• Nov 27th 2013, 09:41 AM
Plato
Re: function help?
Quote:

Originally Posted by eliT
I am so sorry, but I don't know what any of that is. I've spent hours trying to understand. I've done tons of questions (correctly) but I just don't know what to write as the answer to this question. I was seriously hoping someone could tell me what equation or statement actually answers the question that was asked. But so far on three different forums the only replies I get are people asking me questions, giving vague hints I don't understand or telling me to research functions. I'm fairly close to tears now... so tired of trying and only failing to understand.

Do you really want to understand how to do the question?
Do you understand the vertical line test for a function?
That is, the graph of a function cannot contain two ordered pairs with the same first term.
Then what about $\displaystyle \mathcal{G}~?$