a11*x1+a12*x2=b1 a21*x1+a22*x2=b2

$$a_{11} x_{1} + a_{12} x_{2} = b_{1}$$

a21*x1 + a22*x2 = b2

$$a_{21} x_{1} + a_{22} x_{2} = b_{2}$$

$$a_{111} = – frac{1}{x_{1}} left(a_{12} x_{2} – b_{1}right)$$
=
$$frac{1}{x_{1}} left(- a_{12} x_{2} + b_{1}right)$$
=

-(-b1 + a12*x2)/x1

$$a_{211} = – frac{1}{x_{1}} left(a_{22} x_{2} – b_{2}right)$$
=
$$frac{1}{x_{1}} left(- a_{22} x_{2} + b_{2}right)$$
=

-(-b2 + a22*x2)/x1