how to make for loop for newton method

x1=1;
x2=1;
x3=1;
b=[(10*x1)-(2*(x2)^2)+(1*x2)-(2*x3)-5; (8*(x2)^2)+(4*(x3)^2)-9; (8*x2*x3)+4];
a=[10 -4*x(2)+1 -2; 0 16*x(2) 8*x(3);0 8*x(3) 8*x(2)];
inv(a)
c=-(inv(a))*b
xnew=[x1;x2;x3]+c

hai guys please help me. this is my coding for newton method to solve non linear system but i have to solve it until second iteration but i dont know how to do it. so please help me