syms x1; 
syms x2; 
syms x3; 
syms y; 
f(1)=int(y/x3*exp(-y^2/2), y, x3, inf)-x1; 
f(2)=(x2-x1)*exp(-x1^2/2)-x1; 
f(3)=(x3-x2)*exp(-x2^2/2)-x1; 
X=(solve(f));
