sakigirl
Is y=x^2+4 a function? How do you know?
Delete
Share
This Question is Closed
abb0t
Best Response
You've already chosen the best response.
1
Of course it's a function!
abb0t
Best Response
You've already chosen the best response.
1
If it passes the vertical line test, it's a function.
sakigirl
Best Response
You've already chosen the best response.
0
Vertical line test?
sakigirl
Best Response
You've already chosen the best response.
0
I checked the answer key, and it's not a function..
abb0t
Best Response
You've already chosen the best response.
1
|dw:1359706054639:dw|
skullpatrol
Best Response
You've already chosen the best response.
1
Have you checked the definition of a "function"?
sakigirl
Best Response
You've already chosen the best response.
0
yes
skullpatrol
Best Response
You've already chosen the best response.
1
What does does it say?
sakigirl
Best Response
You've already chosen the best response.
0
A function is a special relationship between values: Each of its input values gives back exactly one output value.
skullpatrol
Best Response
You've already chosen the best response.
1
Set up a table of values like ...-3, -2, -1, 0, 1, 2, 3, .. and test it.
sakigirl
Best Response
You've already chosen the best response.
0
How does that let me know whether it's a function or not?
abb0t
Best Response
You've already chosen the best response.
1
buuurn!
sakigirl
Best Response
You've already chosen the best response.
0
lol, it's just a question
skullpatrol
Best Response
You've already chosen the best response.
1
Does each input value give "back exactly one output value."???
sakigirl
Best Response
You've already chosen the best response.
0
Oh, I understand now! Thanks :)
sakigirl
Best Response
You've already chosen the best response.
0
But, won't I have to try out all of the numbers? What if somewhere along the line, the x has more than one y value?
campbell_st
Best Response
You've already chosen the best response.
1
are you sure you haven't entered the equation incorrectly
perhaps it should be
\[x= y^2 + 4\]
sakigirl
Best Response
You've already chosen the best response.
0
No, that is incorrect. The y value is always the output.
abb0t
Best Response
You've already chosen the best response.
1
BUUUUUURN!!!!
sakigirl
Best Response
You've already chosen the best response.
0
omg it's just a correctionnn
campbell_st
Best Response
You've already chosen the best response.
1
no its a graph that looks like
|dw:1359706698575:dw|
sakigirl
Best Response
You've already chosen the best response.
0
Well, that's the reflection of y=x^2+4 over the y axis, but no that's not correct. I have the answer key
skullpatrol
Best Response
You've already chosen the best response.
1
Once you try a few input values you will be able to draw a "graph" like above...
sakigirl
Best Response
You've already chosen the best response.
0
Wait @campbell_st how did you get that graph?
abb0t
Best Response
You've already chosen the best response.
1
campbell_st
Best Response
You've already chosen the best response.
1
It the graph of \[x = y^2 + 4\]
which isn't a function and that's why I asked if you had typed in the correct equation.
Because the equation you have entered for the question is definitely a function...
sakigirl
Best Response
You've already chosen the best response.
0
Oh yes! Yes, that is what I meant.
I have a question for you!
skullpatrol
Best Response
You've already chosen the best response.
1
Once you try a few input values you will be able to draw a "graph" of the output values.
sakigirl
Best Response
You've already chosen the best response.
0
how do you get function for this line? |dw:1359707035624:dw|
sakigirl
Best Response
You've already chosen the best response.
0
*how do you get the function for this line
sakigirl
Best Response
You've already chosen the best response.
0
Like, how did you know it was x=y^2+4?
campbell_st
Best Response
You've already chosen the best response.
1
yep... so as @abb0t said... if you use a vertical line you can see it cuts the curve twice... so its not a function...
if the vertical like only cuts once you have a function...
sakigirl
Best Response
You've already chosen the best response.
0
For all we know, couldn't it have been y=(x+4)^2
sakigirl
Best Response
You've already chosen the best response.
0
?
campbell_st
Best Response
You've already chosen the best response.
1
because you said that the answer was... not a function..
which to me you have transposed the x and y....
just an experience thing
sakigirl
Best Response
You've already chosen the best response.
0
The vertical line test made it so much easier! So @abb0t was correct in the first place :P
campbell_st
Best Response
You've already chosen the best response.
1
and any parabola with x as the independent variable will be a function..
campbell_st
Best Response
You've already chosen the best response.
1
yes he was...
sakigirl
Best Response
You've already chosen the best response.
0
Thank you :) You made it clear for me
abb0t
Best Response
You've already chosen the best response.
1
|dw:1359707283237:dw|
campbell_st
Best Response
You've already chosen the best response.
1
glad to help
skullpatrol
Best Response
You've already chosen the best response.
1
Or the answer key is wrong...the important thing is to know to use the definition:
A function is a special relationship between values: Each of its input values gives back exactly one output value.