The graph above shows a parabola that is symmetric about the x-axis. Which ... ...

The graph above shows a parabola that is symmetric about the x-axis. Which one of the following could be the equation of the graph?


(A)

x = −y2 – 1


(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in Nova Math - Problem Set D: Functions

 
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Posted: 12/24/2011 21:13
Is there a way to plug this equation into a graphing calculator?
 
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Posted: 12/28/2011 07:46
No
Contributor
 
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Posted: 12/28/2011 14:26
Vivian, even though you can't use a graphing calculator, this is a good one to use plugging in and elimination. Plugging in 0 as Y in the equations, we are looking for x= -1

We can eliminate B, because here x= - 0^2 = 0
We can also eliminate C, because here x= -0 + 1 = 1
We can eliminate E, because here x= (0+1)^2 = 1

We are left with A and D. How do we choose between them?
In the graph, the values of x are all negative and lower than -1.
- When we look at equation D, x will have some positive values, i.e.,, when y=2 or y=3 etc. In fact the graph for D is a sideways parabola bottoming out at -1
When we look at equation A, the x values are all negative, consistent with the graph. Try plugging in 1, 2, for example.

Hence the answer is A.
 
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Posted: 02/11/2012 21:19
The produced solution is wrong, the answer is certainly C. Since the graph is moved LEFT, you have to make it (x+1)= -y^2 which is equivalent to x=-y^2 - 1
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Posted: 02/11/2012 21:20
Nvm I'm wrong haha
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Posted: 02/11/2012 21:22
Because C is x= y^2 + 1 not minus 1
 
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Posted: 02/11/2012 21:28
Btw A is incorrect because the graph of A includes a y-intercept at (0,-1) and for multiple other reasons but this one is most evident because you can clearly see it...
 
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Posted: 01/19/2013 16:42
A square is ALWAYS positive, so if the function were x=y^2, the line would be tangent to the y-axis and reflected on the positive x-axis. But in this case the function is negative, so we can eliminate the last two choices.
 
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The graph above shows a parabola that is symmetric about the x-axis. Which ... ... 
Posted: 11/25/2013 23:39
I got it