Problem with solving a system of equations

Question

Wojciech Krawczyk 2015-4-19

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/210346-problem-with-solving-a-system-of-equations

编辑： Wojciech Krawczyk 2015-4-19

I'm trying to solve a system of equations.

cos(fi1)+sin(fi1)=y/33
cos(fi3)+sin(fi3)=18/i3
i3^2+33*i3*cos(fi1-fi3)+i3*cos(fi3)+33^2-30^2+33*x*cos(fi1)+x^2=0
y^2+(x-(30^2-y^2)^(0.5))^2-33^2-i3^2-33*i3*cos(fi1-fi3)==0

5 variables, and 4 equations, but i want to take from it only y(x) function. I put it to matlab, and that is the effect:

fi1 = sym('fi1');
fi3 = sym('fi3');
i3 = sym('i3');
x = sym('x');
y= sym('y');
fi1=(asin(y/33)^2)/2; %calculated from 1st equation
fi3=(asin(18/i3)^2)/2; %calculated from 2nd equation
bocz=solve(i3^2+33*i3*cos(fi1-fi3)+i3*cos(fi3)+33^2-30^2+33*x*cos(fi1)+x^2==0,i3)
przes=solve(y^2+(x-(30^2-y^2)^(0.5))^2-33^2-bocz(1)^2-33*bocz(1)*cos(fi1-fi3)==0,y)

and as a result i get:

Warning: Explicit solution could not be found. 
> In solve at 179
  In czworo at 14 
bocz =
[ empty sym ]
Error using mupadmex
Error in MuPAD command: Index exceeds matrix dimensions.
Error in sym/subsref (line 1580)
        B = mupadmex('symobj::subsref',A.s,inds{:});
Error in czworo (line 20)
przes=solve(y^2+(x-(30^2-y^2)^(0.5))^2-33^2-bocz(1)^2-33*bocz(1)*cos(fi1-fi3)==0,y)