Given 3 lines

$\displaystyle k: a_1x+b_1y+c_1=0$

$\displaystyle l: a_2x+b_2y+c_2=0$

$\displaystyle m: a_3x+b_3y+c_3=0$

Prove that in order to make $\displaystyle k,l,m$ intersect at one point, must satisfy this condition

det$\displaystyle \left[ \begin{matrix} a_1 & b_1 & c_1 \\ a_2 & b_2 & c_2 \\ a_3 & b_3 & c_3 \end{matrix} \right] = 0$