Mohon bantuannya yg no 8 & 9

8) |a .. b| = 4 ==> ad - bc = 4
.... |c .. d|

2 |a ... c| = 2 (ad - bc) = 2 (4) = 8
... |b .. d|

9) |a .. b| = -3 ==> ad - bc = -3
.... |c .. d|

|a + 2c .. b + 2d| = b(a + 2c) - a(b + 2d)
|a ..................... b|

= ab + 2bc - ab - 2ad
= -2 ad + 2bc
= -2 (ad - bc)
= -2 (-3)
= 6