# Finding Angle between 2 points

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aaditya chandel on 20 Apr 2020
Commented: aaditya chandel on 22 Apr 2020
Hello,
I need to calculate the angle between two point from the matlab plot. I tried by applyingthe code which is provided in the discussion but the result is not correct.
The image is attached, I want to find the angle theta which is fromed by point p1,p2 and o.
P1,P2 coordinates are known to us.
I tried using the code provided in the link attached below but the answer is not correct.
I need your help regarding the same.
Awaiting for response.

MaryD on 20 Apr 2020
Do you know the coordinates of O point ? Or anything about that ?
aaditya chandel on 20 Apr 2020
yes the point O coordinates are known.

Gifari Zulkarnaen on 20 Apr 2020
Is this what you mean?
P1 = [10 210];
P2 = [140 210];
Z0 = [(P1(1)+P2(1))/2 225]; % Reference point, assuming it is in the middle of P1 & P2
degree = 2*atand((P2(1)-Z0(1))/(Z0(2)-P2(2)));

aaditya chandel on 20 Apr 2020
The coordinate of Z0 is known.
aaditya chandel on 20 Apr 2020
As shown in the figure P1,P2 and O point coordinates are know.
aaditya chandel on 20 Apr 2020
For this case Z0 appears to be in the middle but it might not be true in other cases.
But its possible to obtain the coordiante.

MaryD on 20 Apr 2020
Edited: MaryD on 20 Apr 2020
r1=sqrt((x1-xo).^2+(y1-yo).^2);
r2=sqrt((x2-xo).^2+(y2-yo).^2);
alpha=acos((x1-xo)/r1);
beta=acos((x2-xo)/r2);
theta=alpha-beta;
keep in mind that acos is specified for pi <0:pi> so if one (or both) points would be placed under O point you have to adjust this equation.

#### 1 Comment

aaditya chandel on 22 Apr 2020
Thanks.