How do you find the axis of symmetry for a quadratic equation y=x2+8x+12?

1 Answer
Jun 6, 2015

y=x2+8x+12

=(x+4)242+12

=(x+4)216+12

=(x+4)24

So the vertex is given by x=4, y=4

... the axis of symmetry being the vertical line x=4

In general, if y=ax2+bx+c then

y=a(x+b2a)2+(cb24a)

which has vertex at (b2a,cb24a)

and axis of symmetry x=b2a