Originally Posted by

**Quacky** I'm not sure I understand completely, but as I understand it:

You are trying to solve this equation for b:

$\displaystyle -b^2+(3x)b+(x^2+1)=0$

By using the vertex-form of a quadratic?

There are a few things I don't understand:

-Where has the variable $\displaystyle d$ come from?

-How have you deduced that $\displaystyle d=\frac{\pm{2}}{\sqrt{13}}$? There is no reference at all to a variable '$\displaystyle d$' in the original equation.

If I had to *guess* I'd say that your "values" for a,b,c refer to the form $\displaystyle ax^2+bx+c$ of a quadratic, although you shouldn't be using "$\displaystyle b$" here to mean two different things so I'm going to call it $\displaystyle b_2$

Sorry, I accidently put a d instead of a b xD

We have:

$\displaystyle a=-1$

$\displaystyle b_2=3x$

$\displaystyle c=x^2+1$

because in this equation, b is the variable we are trying to solve for, **not** x. I don't understand at all which method you are trying to communicate, but **hopefully** this start will help.