[MATLAB基础] 求助！！用solve解方程组出错Error using ==> subsref

[wonderooop]

我想用solve解一个方程组
[a,b,c]=solve('0.0053-0.08*6.35*(sin(pi/4)*cos(a)/sin(a)-cos(pi/4))=0',...
'c-2*15*b*cos(a)=0',...
'0.08*6.35*(sin(pi/4)-sin(a))/sin(a)-(1.4e-4)*(b^(2/3)-(138.6)^(2/3))=0')

但是总是出现错误
??? Error using ==> subsref
Index exceeds matrix dimensions.

Error in ==> sym.subsref at 16
y = builtin('subsref',struct(x),a);

Error in ==> solve at 191
S.(char(symvars(j))) = R(:,j);
好像是超出矩阵的维数，但是找不出原因！！
求助大神帮助！！谢谢！