clc;
clear
syms x y z x1 y1 z1 R a b c z0 ux uy uz
f1=z^2-R^2-x^2-y^2;
f2= (z-z0)^2-c^2+c^2/b^2*y^2+c^2/a^2*x^2;
f3=sym('uy*(x-x1)-ux*(y-y1)');
f4=sym(uz*(x-x1)-ux*(z-z1));
[xa,ya,za]=solve(f1,f3,f4,'x','y','z');
[xb,yb,zb]=solve(f2,f3,f4,'x','y','z');
少打两个*号。稍微修改了下程序