我用matlab的solve函数时总显示出错，请大神帮我修改一下程序

syms f t theta fi T a x v1 v2 n
T=solve('(4.871*10^9)/(1.752*10^6-0.5*a*t^2*fi)^2-f*theta-a*fi=0',...
'f*sqrt(1-theta^2)-*a*sqrt(1-fi^2)',...
'v1-1687.0+a*T*sqrt(1-fi^2)',...
'v2-a*T*fi',...
'12000-0.5*a*fi*T^2','x-(((1687.0-a*T*sqrt(1-fi^2)))^2-1687.0^2)/(2*a*sqrt(1-fi^2)))',...
'57^2-(1687.0+a*T*sqrt(1-fi^2))^2-(a*T*fi)^2',...
'f-2940*n*T','a,fi')

??? Error using ==> solve at 77
' (4.871*10^9)/(1.752*10^6-0.5*a*t^2*fi)^2-f*theta-a*fi=0 ' is not a
valid expression or equation.

Error in ==> Untitled at 2
T=solve('(4.871*10^9)/(1.752*10^6-0.5*a*t^2*fi)^2-f*theta-a*fi=0',...
我想求 T 关于a fi 的函数

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