怎么正确求解符号方程呢?为什么我这个求解过程会出错? E1=sym('Fxc-N*a*[K_tc*(cos(2*phi_

怎么正确求解符号方程呢?
为什么我这个求解过程会出错?
E1=sym('Fxc-N*a*[K_tc*(cos(2*phi_ex)-cos(2*phi_st))-K_rc*((2*phi_ex-2*phi_st)-sin(2*phi_ex)+sin(2*phi_st))]/(8*pi)');
E2=sym('Fyc-N*a*[K_tc*(2*phi_ex-2*phi_st-sin(2*phi_ex)+sin(2*phi_st))-K_rc*(cos(2*phi_ex)-cos(2*phi_st))]/(8*pi)');
[K_tc,K_rc]=solve(E1,E2,K_tc,K_rc)
运行结果是
Warning: 3 equations in 1 variables.
> In solve at 113
In sym.solve at 49
Warning: Explicit solution could not be found.
> In solve at 140
In sym.solve at 49

K_tc =

[ empty sym ]


K_rc =
[]
E1=sym('Fxc-N*a*[K_tc*(cos(2*phi_ex)-cos(2*phi_st))-K_rc*((2*phi_ex-2*phi_st)-sin(2*phi_ex)+sin(2*phi_st))]/(8*pi)=0');
E2=sym('Fyc-N*a*[K_tc*(2*phi_ex-2*phi_st-sin(2*phi_ex)+sin(2*phi_st))-K_rc*(cos(2*phi_ex)-cos(2*phi_st))]/(8*pi)=0');
[K_tc,K_rc]=solve(E1,E2,K_tc,K_rc)