# P2 functionsWatch

This discussion is closed.
#1
Hi

The graph of y=3x^0.5 x>= 0 apparently looks like the sketch i have attached below. I was wondering, why there are no -y values beacuse I thought that if you sqrt a value of x, it gives you both +ve and -ve values for x.

Thanks
0
14 years ago
#2
I know that for it to be a function, ONE value of x must have ONE value of y (by definition) so I would suggest that they are delibarately limiting the range to ensure that it is a useable function in the question where you have encountered it. Sorry I can't be of more help but it has been quite a while since P2.
14 years ago
#3
Yeah, y = sqrt(x) or y = x^(0.5) are limited to positive values only. y = Â±sqrt(x) will give you both positive and negative values for y.

If you want to define both positive and negative values of y, it's better to use a formula like y^2 = x rather than y = x^(0.5)
0
#4
(Original post by Squishy)
Yeah, y = sqrt(x) or y = x^(0.5) are limited to positive values only. y = Â±sqrt(x) will give you both positive and negative values for y.

If you want to define both positive and negative values of y, it's better to use a formula like y^2 = x rather than y = x^(0.5)
But that would give me a quadratic - like x^2, but instead it is y^2 making it an inverted quadratic. So in theory there would be both +ve and -ve y values
0
14 years ago
#5
No, what I mean is that sqrt(x) and x^0.5 are both defined as the positive square root of x only. If you want the negative square root of x, then you need to write -sqrt(x) or -(x^0.5).

However, if you write y^2 = x, then this is the equivalent of saying y = Â±sqrt(x), so you'll get both positive and negative values of y.
0
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