For each quadratic function, find the y-intercept, the equation of the axis of symmetry, and the x-coordinate of the vertex.

Question

f(x)= -2x^2+8x+7

Answer 1

Hi Hailey.

When the equation for a parabola is given in this form, the x-coordinate of the vertex is always:

 

x = -b/2a   so for us that would be (-8)/(-2*(-2)) or -8/4 = -2.  

 

The vertex is at (-2, _____)  Plugging (-2) back into the original equation will give you the y-coordinate of the vertex.  But you were not asked for this.

 

The y-intercept is found by setting all of the x's = 0.  This means the y-intercept is 7.

 

The axis of symmetry is a vertical line through the vertex, or  x=-2  (this is the EQUATION of the axis of symmetry)

 

The x-coordinate of the vertex is -2, same x as the axis of symmetry.