By cross-multiplication, for $a_1 x + b_1 y + c_1 = 0,\; a_2 x + b_2 y + c_2 = 0$, the value of $x$ is —

• a$\dfrac{b_1 c_2 - b_2 c_1}{a_1 b_2 - a_2 b_1}$