det(a1+b1,a2+a2,a3+b3,a4+b4)
=det(a1,a2+a2,a3+b3,a4+b4)+det(b1,a2+a2,a3+b3,a4+b4)
=8det(a1,a2,a3,a4)+8det(b1,a2,a3,a4)
=24-40
=-16
det(a1+b1,a2+a2,a3+b3,a4+b4)
=det(a1,a2+a2,a3+b3,a4+b4)+det(b1,a2+a2,a3+b3,a4+b4)
=8det(a1,a2,a3,a4)+8det(b1,a2,a3,a4)
=24-40
=-16