For any 3 × 3 matrix M, let |M| denote the determinant of M. Let I be the 3 × 3 identity matrix. Let E and F be two 3 × 3 matrices such that (I - EF) is invertible. If G = (I - EF)⁻¹, then which of the following statements is (are) TRUE?
Given: G=(I−EF)−1,I−EF invertible,∣M∣=detM
To find: which of (1)–(4) are TRUE
1. from G=(I−EF)−1: EFG, GEF
2. determinant identity for (1)
3. expand the products for (2), (4)
(I−EF)G=IandG(I−EF)=I
(I−EF)G=I⇒G−EFG=I⇒EFG=G−I
G(I−EF)=I⇒G−GEF=I⇒GEF=G−I
⇒EFG=GEF⇒ (3) TRUE
∣I−EF∣=∣I−FE∣
∣G∣=∣I−EF∣1=∣I−FE∣1
∣FGE∣=∣F∣∣G∣∣E∣=∣FE∣∣G∣=∣I−FE∣∣FE∣
⇒ ∣FE∣=∣I−FE∣∣FGE∣⇒ (1) TRUE
FEFGE=F(EFG)E=F(G−I)E=FGE−FE
(I−FE)(I+FGE)=I+FGE−FE−FEFGE
=I+FGE−FE−(FGE−FE)=I⇒ (2) TRUE
(I−FE)(I−FGE)=I−FGE−FE+FEFGE
=I−FGE−FE+(FGE−FE)=I−2FE=I
⇒ (4) FALSE
True: (1), (2), (3)