Originally Posted by

**Quacky** y=-4x^2-9x-2

Ok, the line will cut the y axis where x=0.

Substitute x=0 into the equation, and you get y=-2. So point of interception is at:

(0,-2)

Now, the line will cut the x axis where y=0. To find this, we can try to factorise:

-4x^2-9x-2=0

4x^2+9x+2=0

(4x+1)(x+2)=0

x=-2 and x=-1/4

x intercepts are

$\displaystyle (-2,0)$ and $\displaystyle (-1/4,0)$

Parabolas are symmetrical, so if you take the x intercepts, the line of symmetry will be halfway between them.

$\displaystyle -2.25/2 = -1.125$ (wow, nasty numbers)

x=-1.125 is the line of symmetry.

A question about the vertex: Have you covered differentiation?