# Finding the intersec point using InterX?

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ErikJon Pérez Mardaras on 21 Oct 2020
Commented: ErikJon Pérez Mardaras on 25 Oct 2020 at 18:14
I am trying to find the intersect point of two lines using "InterX".
More concretely, I want to find the intersect point of the line L1 which two coordinates are x1=1,y1=1 and x2=3 y2=6
and the line L2 which two coordinates are x1=-2 y1=8 and x2=2 y2=-1
I don´t know if I understanded well the "InterX" function, but here is the code I have executed:
hold on
x=linspace(-30,30)
L1=[1 3;
1 6]
L2=[-2 2;
8 -1]
P=InterX(L1,L2);
plot(L1)
plot(L2)
plot(P,'ro')
And the result Matlab gives to me is completly absurd, in the following image:
What am I doing wrong? How can I properly use the "InterX" function? I have searched in the community but I didn´t understand it very well as you can see

KSSV on 21 Oct 2020
Edited: KSSV on 21 Oct 2020
You should read the documentation/ help given in the InterX function. Your curves/ data points should be such that :
L1 = [x11 x12 ; y11 y12] ;
L2 = [x21 x22 ; y21 y22] ;
L1=[1 3;
1 6]
L2=[-2 2;
8 -1]
P=InterX(L1,L2);
figure
hold on
plot(L1(1,:),L1(2,:),'r')
plot(L2(1,:),L2(2,:),'b')
plot(P(1),P(2),'ro')

ErikJon Pérez Mardaras on 23 Oct 2020
And how it would be if I would like to know all intersect points between two elements?. For instance, let's say I would like to know the two intersec points between a line and a circle as shown below.
I don`t know why matlab only shows me one point of intersec. I have read the "help" text of "InterX" function but I think I didn´t get it. Here is the code I have introduced:
How can I find both points of intersec?
axis equal
hold on
caca=2*pi();
ang=linspace(0,caca);
xp=5*cos(ang);
yp=5*sin(ang);
circ=[xp;yp];
plot(xp,yp,'r');
L1=[-7 7; 2 2];
plot(L1(1,:),L1(2,:),'b')
P=InterX(circ,L1);
plot(P(1),P(2),'go');
KSSV on 23 Oct 2020
You are getting two points. You are plotting it wrong.
plot(P(1,:),P(2,:),'go');
ErikJon Pérez Mardaras on 25 Oct 2020 at 18:14
thanks!

R2019b

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