GMAT Math : Graphing a quadratic function

Study concepts, example questions & explanations for GMAT Math

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Example Questions

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Example Question #671 : Sat Mathematics

The parabolas of the functions  and  on the coordinate plane have the same vertex.

If we define , which of the following is a possible equation for  ?

Screen shot 2016 02 10 at 12.25.12 pm

Possible Answers:

None of the other responses gives a correct answer.

Correct answer:

Explanation:

The eqiatopm of  is given in the vertex form

,

so the vertex of its parabola is . The graphs of  and  are parabolas with the same vertex, so they must have the same values for  and 

For the function ,  and .

Screen shot 2016 02 10 at 12.25.12 pm

Of the five choices, the only equation of   that has these same values, and that therefore has a parabola with the same vertex, is .

Screen shot 2016 02 10 at 12.27.19 pm

To verify, graph both functions on the same grid.

Screen shot 2016 02 10 at 12.28.14 pm

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