What is the "formula" for finding the axis of symmetry? 

Find the vertex for  $y=x^2-8x+15$  

Find the axis of symmetry of
 $y=3x^2-6x+4$  

Find the vertex of  $y=3x^2-6x+4$   

Find the axis of symmetry for  $y=-x^2-4x+12$  

Find the vertex of  $y=-x^2-4x+12$  

Find the axis of symmetry of  $y=-2x^2-16x+3$  

Find the vertex of   $y=-2x^2-16x+3$  

Find the axis of symmetry of  $y=x^2+16x+71$  

Find the vertex  $y=x^2+16x+71$  

 Find the axis of symmetry of
 $y=x^2-2x-5$  

Find the vertex   $y=x^2-2x-5$