You can subtract two points to obtain a vector:
Make a vector \vec{OA} by doing A-O, where O=(0,0), then actually \vec{OA} becomes (0,4).
Then let S be the centre of the circle, so S = (-3,0)
And make a vector pointing from A to S \vec{AS} = S - A = (-3,-4)
Then just use add vectors...
I'd like to know how to find relations between coefficients of a polynomial p(x) so that equation p(x) = 0 has only real roots.
For example I have quadratic equation:
x^{2}+px+q = 0
then the Discriminant must be >= 0 so p^{2} >= 4q
But I need to find it for equations of higher power...