The best way to solve a quadratic function is to put brackets into the equation.
Start with an example
Find x when y=0 for the function
y=x*2 + 5x + 6
As y=0 make the whole equation= 0:
x*2 + 5x + 6=0
Try and put this into brackets:
(x+a)(x+b)=0 (as all the values are positive, we know that there are going to be no negative signs in the brackets).
Now we just need to find values for a and b that multiply out to give us the equation we need.
Try a=6 and b=1:
This gives us the 6 at the end but when multiplied out gives us 7x- which is too much.
Now try a=2 and b=3 and multply out:
We get 0=x2+ 2x + 3x + 6= x2 + 5x + 6 ... which is what we want!
So we get (x+2)(x+3)=0
For it to equal 0 either:
x+2=0 so x=-2 or
x+3=0 so x=-3
so x=-2, -3