The angle between the lines 2x = 3y = –z and 6x = –y = – 4z is

Given lines are 

$\frac{x}{3}=\frac{y}{2}=\frac{z}{-6}$………… (1)

$\frac{x}{2}=\frac{y}{-12}=\frac{z}{-3}$……. (2)

If $\theta$ is the required angle $a_1{a}_2+b_1{b}_2+c_1{c}_2=0$, $\theta =\frac{\pi }{2}$