Posted by Gina on Saturday, September 13, 2008 at 6:13pm.
Determine whether y is a function of x:
x^2yx^2+4y=0
Please help. Thanks.

precalculus  David Q, Saturday, September 13, 2008 at 6:23pm
Do you mean "Can y be expressed as a function of x?". If so then the answer is yes it can, if by "x^2y" you mean "x²y" and not "x raised to the power of 2y". The equation x²y  x² + 4y = 0
can be written as (x²+4)y = x², from which you can easily express either x in terms of y, or y in terms of x. 
precalculus  Damon, Saturday, September 13, 2008 at 6:28pm
well, you can write y as a function of x, and get one and only one value of y for every x
however x is not a function of y because there are two values of x for every y. 
precalculus  David Q, Saturday, September 13, 2008 at 6:42pm
Fair enough, though you could presumably define a function by restricting the range to just zero plus either the positive or negative real numbers.

precalculus  Gina, Saturday, September 13, 2008 at 7:17pm
So the answer is yes?

precalculus  David Q, Sunday, September 14, 2008 at 6:00am
The answer is yes: you can write y as a function of x. Damon and I were debating whether you can write x as a function of y, which wasn't what you were asked.

precalculus  Gina, Sunday, September 14, 2008 at 11:28am
How exactly do you know that you can get one and only one value of y for every x?

precalculus  Anonymous, Sunday, September 14, 2008 at 12:27pm
There's only one value for y because your original equation (x^2yx^2+4y=0) can be rewritten as (x²+4)y = x². Or, by dividing both sides by (x²+4),
y = x²/(x²+4)
Feed any value of x into the righthand side, and you'll get exactly one value for y. 
precalculus  Gina, Sunday, September 14, 2008 at 2:19pm
OH thanks, gotcha!