Thread Subject: Intersection between line and half-circle

How do I find the intersections between a line and a circle? If I do it by hand, I end up with:

y = mx +b (line equation)
(x-h)^2 + (y- k)^2 = r^2 (circle equation)

do some algebra...

(x-h)^2 + (mx + b - k )^2 = r^2

(x-h)^2 = r^2 - (mx +b -k)^2

How do I make Matlab get x for me?

On 8 Nov, 06:37, "Catherine Szeto" <catsz...@gmail.com> wrote:
> How do I find the intersections between a line and a circle? If I do it by hand, I end up with:
>
> y = mx +b (line equation)
> (x-h)^2 + (y- k)^2 = r^2   (circle equation)
>
> do some algebra...
>
> (x-h)^2 + (mx + b - k )^2 = r^2
>
> (x-h)^2 = r^2 - (mx +b -k)^2
>
> How do I make Matlab get x for me?

1) Write out the expression as a 2nd order polynomial in x
2) Write out the standard formula for solving 2nd order
   polynomials
3) Find the numbers that go into the formulas
4) Have matlab compute the answers from the formulas and
   numbers

Rune

Rune Allnor <allnor@tele.ntnu.no> wrote in message <0727aeb3-86d2-42f3-b629-4fb12f55a557@d5g2000yqm.googlegroups.com>...
> On 8 Nov, 06:37, "Catherine Szeto" <catsz...@gmail.com> wrote:
> > How do I find the intersections between a line and a circle? If I do it by hand, I end up with:
> >
> > y = mx +b (line equation)
> > (x-h)^2 + (y- k)^2 = r^2 ? (circle equation)
> >
> > do some algebra...
> >
> > (x-h)^2 + (mx + b - k )^2 = r^2
> >
> > (x-h)^2 = r^2 - (mx +b -k)^2
> >
> > How do I make Matlab get x for me?
>
> 1) Write out the expression as a 2nd order polynomial in x
> 2) Write out the standard formula for solving 2nd order
> polynomials
> 3) Find the numbers that go into the formulas
> 4) Have matlab compute the answers from the formulas and
> numbers
>
> Rune

Thanks, I got it working. Turns out I was using a function wrong.