What is the axis of symmetry formula?

Answer 1

-b/2a. i think.
To show this, consider this equation:

y = ax² + bx + c

Factor out the a:

y = a(x² + bx/a + c/a)

Then, complete the squares to get:

y = a(x² + bx/a + (b/(2a))² + c/a - (b/(2a))²)

= a((x + (b/2a))² + c/a - (b/(2a))²)

= a(x + (b/2a))² + c - b/(4a)

By the vertex form:

y = a(x - h)² + k where x = h is the axis of symmetry.

So the general axis of symmetry for the quadratic equation is x = -b/(2a).