一旦cos普赛里不含有未知数，mathematica就可以瞬间出结果。反之有了未知数之后就解不出来。代码如下：
r = 0.036;
Subscript[Z, B] = 50;
Subscript[X, 7] = 1;
P = 4;
\[Alpha] = 0.4;
Solve[{(4 *Subscript[X, 1])/(\[Pi]*Sqrt[
Subscript[X, 1]^2 + Subscript[X, 2]^2]) - (r Subscript[X, 1])/
Subscript[Z, B] + f*Subscript[X, 2] - Subscript[X, 3] -
Subscript[X, 5] == 0,
-f*Subscript[X, 1] - Subscript[X, 4] - Subscript[X, 6] - (
r*Subscript[X, 2])/Subscript[Z, B] == 0,
(1 - \[Alpha])*Subscript[X, 1] + f*Subscript[X, 4] == 0,
(1 - \[Alpha])*Subscript[X, 2] - f*Subscript[X, 3] == 0,
((1 + Cos[\[Psi]])*Sqrt[
Subscript[X, 1]^2 + Subscript[X, 2]^2])/\[Pi] == P,
Cos[\[Psi]] == 1 - (2*f)/(\[Alpha]*((P*\[Pi])/2 + f/\[Alpha])),
\[Mu] == \[Psi] - Sin[\[Psi]] Cos[\[Psi]],
Subscript[X,
5] == \[Alpha]/(\[Pi]*
f) (Subscript[X, 1]*Sin[\[Psi]]^2 + Subscript[X, 2]*\[Mu]),
Subscript[X,
6] == \[Alpha]/(\[Pi]*
f) (Subscript[X, 2]*Sin[\[Psi]]^2 - Subscript[X, 1]*\[Mu]),
0 < f < 2.5}, f];

三角函数固然可能造成问题，但你这个显然还有更严重的问题吧？你觉得为什么下面这个方程Mathematica出不了结果？：
Solve[{a == 1, b == 2}, a]
想知道原因的话，搜一下MaxExtraConditions的帮助。

Clear;
r1 = 0.2;
L = 3;
a = 8.38;
v = -6.21;
b = -6.23;
c = -1.65;
U = 1.2;
Solve[U*(\[Omega]R*\[Omega]i)/(\[Omega]R^2 + \[Omega]i^2)^2 -
c*(\[Omega]R/
b^2 + (\[Omega]R*\[Omega]i)/
b^3*(Log[(b*r1*L - \[Omega]i)^2 + \[Omega]R^2] -
Log[(b*r1 - \[Omega]i)^2 + \[Omega]R^2]) == -((\[Omega]R^2 \
+ \[Omega]i^2)/
b^3)*(1/Tan[\[Omega]R/(b*r1*L - \[Omega]i)] - 1/
Tan[\[Omega]R/(b*r1 - \[Omega]i)])) &&
a + v*1/(\[Omega]R^2 + \[Omega]i^2) +
c*(\[Omega]i/
b - (\[Omega]R^2 + \[Omega]i^2)/(
2*b^3)*(Log[(b*r1*L - \[Omega]i)^2 + \[Omega]R^2] -
Log[(b*r1 - \[Omega]i)^2 + \[Omega]R^2]) == -((
2*\[Omega]R*\[Omega]i)/(
c*b^3))*(1/Tan[\[Omega]R/(b*r1*L - \[Omega]i)] - 1/
Tan[\[Omega]R/(b*r1 - \[Omega]i)])), {\[Omega]R, \[Omega]i}]
请问这样含有三角函数和对数的方程组，Mathe为何求解不出？