# How to find angle between two lines?

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Beulah A am 21 Okt. 2019
Verschoben: Dyuman Joshi am 9 Jan. 2024
For example, there is line L1 between two points (x1,y1) and (x2,y2). Another line L2 between points (x1,y1) and (x3,y3). I want to find the angle between the lines L1, L2. How to find in MATLAB? I think in matlab there is no predefined function which performs the same.
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James Tursa am 21 Okt. 2019
sudeep am 7 Jan. 2024
Verschoben: Dyuman Joshi am 9 Jan. 2024
TURE AND
Example 1: Find the angle between r1 = 2(1 + cost) and r23(1-cost) and plot the graph for the same.

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### Akzeptierte Antwort

Bjorn Gustavsson am 21 Okt. 2019
A more stable method that what Jos suggested is
v_1 = [x2,y2,0] - [x1,y1,0];
v_2 = [x3,y3,0] - [x1,y1,0];
Theta = atan2(norm(cross(v_1, v_2)), dot(v_1, v_2));
HTH
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jari jafri am 4 Okt. 2023
Bearbeitet: jari jafri am 4 Okt. 2023
I got my V_1 and V_2 vectors as
v_1 =
1×3 int32 row vector
-633 990 0
v_2 =
1×3 int32 row vector
0 500 0
But i am having the following error so I 'm looking for how to remove this error
Error using norm
First argument must be single or double.
Error in test6 (line 64)
Theta = atan2(norm(cross(v_1, v_2)), dot(v_1, v_2));
I'm getting this error while using this code
Dyuman Joshi am 4 Okt. 2023
@jari jafri convert the data to double -
v_1 = int32([-633 990 0]);
v_2 = int32([0 500 0]);
v_1 = double(v_1);
v_2 = double(v_2);
Theta = atan2(norm(cross(v_1, v_2)), dot(v_1, v_2))
Theta = 0.5689

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### Weitere Antworten (2)

Jos (10584) am 21 Okt. 2019
Use the dot product between the two vectors (v1 and v2) given by the four x,y pairs points.
Given the formula: dot(v1,v2) = | v1 | x | v2 | x cos(A)
I leave it to you to find the angle A using the matlab functions norm, dot and acos.
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Bjorn Gustavsson am 21 Okt. 2019
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