Which of these functions represents a quadratic function and why?
y=-x^2+16sqrtx-64
x=y^2-2y+4
-5+3y=-4
y=3x^2-5x+9

Question

Which of these functions represents a quadratic function and why?
y=-x^2+16sqrtx-64
x=y^2-2y+4
-5+3y=-4
y=3x^2-5x+9

campbell_st · Answer

its an interesting question... as they aren't all functions...

cutiecomittee123 · Answer

Yeah true

cutiecomittee123 · Answer

But which one is quadratic

campbell_st · Answer

so do you know the general form for a quadratic..?

cutiecomittee123 · Answer

y=x^2+x-constant

campbell_st · Answer

well the general form is 

$$y = ax^2 + bx + c$$

cutiecomittee123 · Answer

I think that the last one is the quadratic function because reading it from right to left it goes downwards in value of x until it gets to the constant

campbell_st · Answer

so which equations fit this form...?

campbell_st · Answer

so that's good... but what about the 2nd one...?

cutiecomittee123 · Answer

Well I thin that it doesnt work because it starts with x= and y cannot be used as a quadratic equation?

anonymous · Answer

the answer is y=3x^2-5x+9

cutiecomittee123 · Answer

Thanks I got it right and I understand:)

campbell_st · Answer

well it can start with anything you like and contain and variable you like... 

by the problem is the 2nd one is not a function... 

if you graphed it you would see something like this...

|dw:1433713794806:dw|

which fails the vertical line test for a function... I'd expect you know about that