Select the x-coordinate of the vertex of the parabola defined by the function f(x) = -7x2 + 3x + 1.

Question

Answers:

A. -7/3

B. 1

C. 3/14

D. -3/7

 

Answer 1

Hi Carmalita;

f(x) = -7x² + 3x + 1

There are two techniques to calculate the x-coordinate of the vertex...

x=-b/2a

x=-3/[(2)(-7)]

x=-3/-14

x=3/14

 

or

 

Take the first derivative of the equation and set to zero.   We are setting to zero because the vertex is the point at which there is no change of slope...

0=-14x+3

-3=-14x

-3/-14=x

3/14=x

 

ANSWER IS C.

Answer 2

f( x) = -7X^2 + 3X +1

 

   Vertex ( - b/ 2a, f( -b/2a)) 

 

             = ( - 3/ -14, f ( 3/14))

 

              = ( 3/14, f( 3/14)

 

         C is the correct answer.

       

Answer 3

Hi,

       The x coordinate of the vertex is at the axis of symmetry  if the equation of the parabola is ax²+bx+c the the axis is at x=-b/2a. In the example a=-7 b=3 so x=3/14. So the answer is C

 

Jim