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how can i determine angle between 2 variables

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Opariuc Andrei
Opariuc Andrei on 5 Jan 2021
Answered: the cyclist on 5 Jan 2021
how can i do/calculate the angle like in the ss below ,i know rBx,rBy and g
g=180/pi;
teta1=300;teta2=320;teta3=40;teta4=100;teta5=160; % in degrees
Alfa=deg2rad(teta1/g);aLfa=deg2rad(teta2/g); alFa=deg2rad(teta3/g);alfA=deg2rad(teta4/g);alfa=deg2rad(teta5/g);
rBx=-1*(r1*cos(Alfa)+r2*cos(aLfa)+r3*cos(alFa)+r4*cos(alfA)+r5*cos(alfa)+rAx)
rBy=-1*(r1*sin(Alfa)+r2*sin(aLfa)+r3*sin(alFa)+r4*sin(alfA)+r5*sin(alfa)+rAy)

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Opariuc Andrei
Opariuc Andrei on 5 Jan 2021
i knew about atan2 and i tried it before i posted but it did not gave the correct answear , i did a backtrace from the course pdf and got everything right/ identical up until alfaBg or where i'm supposed to do/find angle
%% input
%% values r, values z, values alfa_gi
r1=154; z1=30; ag1=267;
r2=122; z2=68; ag2=325;
r3=63; z3=105; ag3=49;
r4=68; z4=144; ag4=118;
r5=126; z5=188; ag5=180;
zA=226;
%% calculus
g=180/pi;
alfa1=ag1/g;
alfa2=ag2/g;
alfa3=ag3/g;
alfa4=ag4/g;
alfa5=ag5/g;
%% rAx si rAy
disp("rAx si rAy")
rAx=(-1)*(r1*z1*cos(alfa1)+r2*z2*cos(alfa2)+r3*z3*cos(alfa3)+r4*z4*cos(alfa4)+r5*z5*cos(alfa5))/zA
rAy=(-1)*(r1*z1*sin(alfa1)+r2*z2*sin(alfa2)+r3*z3*sin(alfa3)+r4*z4*sin(alfa4)+r5*z5*sin(alfa5))/zA
rA=sqrt(rAx^2+rAy^2) which results in 79.234 like in my pdf (value i'm supposed to get) but when i applied atan2(rAx,rAy)*g i was supposed to get the value in the ss 346.217
but instead i got alfa_A_g =103.7827 , i also tried doing deg2rad and rad2deg(atan2(...)) and didn't get the desired result

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Answers (1)

the cyclist
the cyclist on 5 Jan 2021
You got the order of the inputs incorrect. It should be
atan2(rAy,rAx)*g
This will give a negative answer, measuring the angle "down" from the x-axis. If you add 360deg, you'll get the answer you want.

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