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sakigirl

  • 3 years ago

Is y=x^2+4 a function? How do you know?

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  1. abb0t
    • 3 years ago
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    Of course it's a function!

  2. abb0t
    • 3 years ago
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    If it passes the vertical line test, it's a function.

  3. sakigirl
    • 3 years ago
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    Vertical line test?

  4. sakigirl
    • 3 years ago
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    I checked the answer key, and it's not a function..

  5. abb0t
    • 3 years ago
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    |dw:1359706054639:dw|

  6. skullpatrol
    • 3 years ago
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    Have you checked the definition of a "function"?

  7. sakigirl
    • 3 years ago
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    yes

  8. skullpatrol
    • 3 years ago
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    What does does it say?

  9. sakigirl
    • 3 years ago
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    A function is a special relationship between values: Each of its input values gives back exactly one output value.

  10. skullpatrol
    • 3 years ago
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    Set up a table of values like ...-3, -2, -1, 0, 1, 2, 3, .. and test it.

  11. sakigirl
    • 3 years ago
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    How does that let me know whether it's a function or not?

  12. abb0t
    • 3 years ago
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    buuurn!

  13. sakigirl
    • 3 years ago
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    lol, it's just a question

  14. skullpatrol
    • 3 years ago
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    Does each input value give "back exactly one output value."???

  15. sakigirl
    • 3 years ago
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    Oh, I understand now! Thanks :)

  16. sakigirl
    • 3 years ago
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    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?

  17. campbell_st
    • 3 years ago
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    are you sure you haven't entered the equation incorrectly perhaps it should be \[x= y^2 + 4\]

  18. sakigirl
    • 3 years ago
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    No, that is incorrect. The y value is always the output.

  19. abb0t
    • 3 years ago
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    BUUUUUURN!!!!

  20. sakigirl
    • 3 years ago
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    omg it's just a correctionnn

  21. campbell_st
    • 3 years ago
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    no its a graph that looks like |dw:1359706698575:dw|

  22. sakigirl
    • 3 years ago
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    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

  23. skullpatrol
    • 3 years ago
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    Once you try a few input values you will be able to draw a "graph" like above...

  24. sakigirl
    • 3 years ago
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    Wait @campbell_st how did you get that graph?

  25. abb0t
    • 3 years ago
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  26. campbell_st
    • 3 years ago
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    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...

  27. sakigirl
    • 3 years ago
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    Oh yes! Yes, that is what I meant. I have a question for you!

  28. skullpatrol
    • 3 years ago
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    Once you try a few input values you will be able to draw a "graph" of the output values.

  29. sakigirl
    • 3 years ago
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    how do you get function for this line? |dw:1359707035624:dw|

  30. sakigirl
    • 3 years ago
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    *how do you get the function for this line

  31. sakigirl
    • 3 years ago
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    Like, how did you know it was x=y^2+4?

  32. campbell_st
    • 3 years ago
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    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...

  33. sakigirl
    • 3 years ago
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    For all we know, couldn't it have been y=(x+4)^2

  34. sakigirl
    • 3 years ago
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    ?

  35. campbell_st
    • 3 years ago
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    because you said that the answer was... not a function.. which to me you have transposed the x and y.... just an experience thing

  36. sakigirl
    • 3 years ago
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    The vertical line test made it so much easier! So @abb0t was correct in the first place :P

  37. campbell_st
    • 3 years ago
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    and any parabola with x as the independent variable will be a function..

  38. campbell_st
    • 3 years ago
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    yes he was...

  39. sakigirl
    • 3 years ago
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    Thank you :) You made it clear for me

  40. abb0t
    • 3 years ago
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    |dw:1359707283237:dw|

  41. campbell_st
    • 3 years ago
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    glad to help

  42. skullpatrol
    • 3 years ago
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    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.

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