How to calculate a angle between two vectors in 3D

Hi, I have a question, I have a table with 12 reference points

if true
% POINT  X  Y  Z
1  0  0  0
2  70.5  0  0
3  141  0  0
4  141  0  141.5
5  70.5  0  141.5
6  0  0  141.5
7  0  137.5  0
8  70.5  137.5  0
9  141  140  0
10  141  141.5  141.5
11  70.5  139  141.5
12  0  141.5  141.5

end

The segment 1 is defined by the point 1 and point 2 and the segment 2 is defined by the point 1 and point 7. I am able to calculate the angle with the following rotine,

if true
  % angle_x1_x13 = atan2(norm(cross(v1,v2)),dot(v1,v2));
    anglout = radtodeg(angle_x1_x13); 
end

The result is ~90º and this result is correct if I think in xy plan, but I need to calculate the angle to yz plan and xz plan. Anyone help me?

NOTE:-

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This code uses your angle calculation and shows for different reference points (3d). 2d is the same for your formula.

% Origin is reference point
p1 = 1*ones(1,3); % directly v1 = p1 
p2 = 2*ones(1,3); % directly v2 = p2
% With origin as the reference point, the angle between vectors is 0
ang = rad2deg(atan2(norm(cross(p1,p2)),dot(p1,p2)));
disp(ang)
% Choosing reference point such that new v1, v2 are at 90 degrees
refpoint = [2 2 1];

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How to calculate a angle between two vectors in 3D

How to calculate a angle between two vectors in 3D