[smiles860710]

>> syms x m
>> x=solve(9.8*(x^2)*log(1-(20*2.9648*4*pi)/(9.8*m))/(2.9648^2*(4*pi)^2)-(20*m)/(2.9648*4*pi)-500)
这样就得到
x =

25/13601079296/log(1/1225*(1225*m-29648*pi)/m)/pi*2828041497789715429^(1/2)*(log(1/1225*(1225*m-29648*pi)/m)*pi*(25*m+7412*pi))^(1/2)
-25/13601079296/log(1/1225*(1225*m-29648*pi)/m)/pi*2828041497789715429^(1/2)*(log(1/1225*(1225*m-29648*pi)/m)*pi*(25*m+7412*pi))^(1/2)