TeX джерело:

{\;\;\left \{ \begin{array}{rcl}A(x-x_1)+\,B(y-y_1)+\,C(z-z_1)\,&=&0\\A(x_2-x_1)+B(y_2-y_1)+C(z_2-z_1)&=&0\\A(x_3-x_1)+B(y_3-y_1)+C(z_3-z_1)&=&0 \end{array}\right.}