## stupidinmath 2 years ago are parabolas that open to the right / left quadratic functions too?

1. UnkleRhaukus

parabolas that open to the left are right are not functions, they are relations

2. UnkleRhaukus

a function can only have a single output for the each input a test for this is the vertical line test, which say that on the graph of a relation, if any vertical line touches the line of the relation at more than one place the the relation is not a function |dw:1356789558553:dw|

3. stupidinmath

THANK YOU, SO MUCH! ;D

4. UnkleRhaukus

i would say that $$x=y^2$$ is a quadratic relation though

5. UnkleRhaukus

kinda similar is $y=\sqrt x$ |dw:1356789914537:dw| which only has one output for each input and thus passes the vertical line test so $y=\sqrt x$ is a function

6. UnkleRhaukus

These relations are different so you'll have to remember to be carful if you want to rearrange the first relation $y^2=x$$y=+\sqrt x,-\sqrt x$$\quad=±\sqrt x$ which is clearly not a function as it has two values for most inputs