1. Division of matrix
1. `A/B=A*B^-1`
2. `B/A=B*A^-1`
Examples
1. Find `B/A` ...
`A=[[2,3,1],[0,5,6],[1,1,2]]`,`B=[[2,1,-1],[1,0,-1],[1,1,2]]`
Solution:
`|A|` | = | | `2` | `3` | `1` | | | `0` | `5` | `6` | | | `1` | `1` | `2` | |
|
`=2 xx (5 × 2 - 6 × 1) -3 xx (0 × 2 - 6 × 1) +1 xx (0 × 1 - 5 × 1)`
`=2 xx (10 -6) -3 xx (0 -6) +1 xx (0 -5)`
`=2 xx (4) -3 xx (-6) +1 xx (-5)`
`= 8 +18 -5`
`=21`
`Adj(A)` | = | Adj | | `2` | `3` | `1` | | | `0` | `5` | `6` | | | `1` | `1` | `2` | |
|
|
= | | `+(5 × 2 - 6 × 1)` | `-(0 × 2 - 6 × 1)` | `+(0 × 1 - 5 × 1)` | | | `-(3 × 2 - 1 × 1)` | `+(2 × 2 - 1 × 1)` | `-(2 × 1 - 3 × 1)` | | | `+(3 × 6 - 1 × 5)` | `-(2 × 6 - 1 × 0)` | `+(2 × 5 - 3 × 0)` | |
| T |
|
= | | `+(10 -6)` | `-(0 -6)` | `+(0 -5)` | | | `-(6 -1)` | `+(4 -1)` | `-(2 -3)` | | | `+(18 -5)` | `-(12 +0)` | `+(10 +0)` | |
| T |
|
= | | `4` | `6` | `-5` | | | `-5` | `3` | `1` | | | `13` | `-12` | `10` | |
| T |
|
= | | `4` | `-5` | `13` | | | `6` | `3` | `-12` | | | `-5` | `1` | `10` | |
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`"Now, "A^(-1)=1/|A| × Adj(A)`
= | `1/(21)` × | | `4` | `-5` | `13` | | | `6` | `3` | `-12` | | | `-5` | `1` | `10` | |
|
= | | `0.1905` | `-0.2381` | `0.619` | | | `0.2857` | `0.1429` | `-0.5714` | | | `-0.2381` | `0.0476` | `0.4762` | |
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`B×(A^(-1))` | = | | `2` | `1` | `-1` | | | `1` | `0` | `-1` | | | `1` | `1` | `2` | |
| × | | `0.1905` | `-0.2381` | `0.619` | | | `0.2857` | `0.1429` | `-0.5714` | | | `-0.2381` | `0.0476` | `0.4762` | |
|
= | | `2×0.1905+1×0.2857-1×-0.2381` | `2×-0.2381+1×0.1429-1×0.0476` | `2×0.619+1×-0.5714-1×0.4762` | | | `1×0.1905+0×0.2857-1×-0.2381` | `1×-0.2381+0×0.1429-1×0.0476` | `1×0.619+0×-0.5714-1×0.4762` | | | `1×0.1905+1×0.2857+2×-0.2381` | `1×-0.2381+1×0.1429+2×0.0476` | `1×0.619+1×-0.5714+2×0.4762` | |
|
= | | `0.381+0.2857+0.2381` | `-0.4762+0.1429-0.0476` | `1.2381-0.5714-0.4762` | | | `0.1905+0+0.2381` | `-0.2381+0-0.0476` | `0.619+0-0.4762` | | | `0.1905+0.2857-0.4762` | `-0.2381+0.1429+0.0952` | `0.619-0.5714+0.9524` | |
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= | | `0.9048` | `-0.381` | `0.1905` | | | `0.4286` | `-0.2857` | `0.1429` | | | `0` | `0` | `1` | |
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This material is intended as a summary. Use your textbook for detail explanation.
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