# Thread: Help with math extension 2 question, thanks!

1. ## Help with math extension 2 question, thanks!

Let H and K be the points representing the roots of
x^2 +2px+q=0, where p and q are real and p^2 <q . Find the algebraic relation satisfied by p and q in each of the following cases
(i) angle HOK is a right angle.
(ii) A, B, H and K are equidistant from the origin.

2. ## Re: Help with math extension 2 question, thanks!

This question should go in the Maths subforum.

$x = -p \pm \sqrt{p^2-q}$

Because $p^2 - q < 0$, we can use the identity $\sqrt{ab} = \sqrt a \sqrt b$ with $a = -1$ and $b = q - p^2$.

(Note that this identity is not valid if both $a$ and $b$ are negative)

Hence,

$x = -p \pm i\sqrt{q-p^2}$

Where $p$ and $\sqrt{q-p^2}$ are both real numbers.

Therefore, the gradient of the line joining the root to the origin in the complex plane is given by

$m = \pm \frac{\sqrt{q-p^2}}{p}$

And recall that the requirement for two lines to be perpendicular is that their gradients multiply to be $-1$.

The rest should be easy.

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