1. Definition and Examples
Minor of a matrix `(2 xx 2)`
`|A|=|[a,b],[c,d]|`
minor of `a = d`
minor of `b = c`
minor of `c = b`
minor of `d = a`
Minor of a matrix `(3 xx 3)`
`|A|=|[a,b,c],[d,e,f],[g,h,i]|`
minor of `a = |[e,f],[h,k]|`
minor of `b = |[d,f],[g,k]|`
minor of `c = |[d,e],[g,h]|`
minor of `d = |[b,c],[h,i]|`
minor of `e = |[a,c],[g,i]|`
minor of `f = |[a,b],[g,h]|`
minor of `g = |[b,c],[e,f]|`
minor of `h = |[a,c],[d,f]|`
minor of `i = |[a,b],[d,e]|`
`A=[[1,2,3],[4,5,6],[7,8,9]]`
minor of `1 = A_11 = |[5,6],[8,9]| = 45-48 = -3`
minor of `2 = A_12 = |[4,6],[7,9]| = 36-42 = -6`
minor of `3 = A_13 = |[4,5],[7,8]| = 32-35 = -3`
minor of `4 = A_21 = |[2,3],[8,9]| = 18-24 = -6`
minor of `5 = A_22 = |[1,3],[7,9]| = 9-21 = -12`
minor of `6 = A_23 = |[1,2],[7,8]| = 8-14 = -6`
minor of `7 = A_31 = |[2,3],[5,6]| = 12-15 = -3`
minor of `8 = A_32 = |[1,3],[4,6]| = 6-12 = -6`
minor of `9 = A_33 = |[1,2],[4,5]| = 5-8 = -3`
The minor matrix of A is `[A_(ij)]=[[A_11,A_12,A_13],[A_21,A_22,A_23],[A_31,A_32,A_33]]
=[[-3,-6,-3],[-6,-12,-6],[-3,-6,-3]]`
Examples
1. Find `"Minor"(A)` ... `A=[[3,1,1],[-1,2,1],[1,1,1]]`
Solution:
`MINOR(A)` | = | `MINOR` | | `3` | `1` | `1` | | | `-1` | `2` | `1` | | | `1` | `1` | `1` | |
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= | | `2 × 1 - 1 × 1` | `-1 × 1 - 1 × 1` | `-1 × 1 - 2 × 1` | | | `1 × 1 - 1 × 1` | `3 × 1 - 1 × 1` | `3 × 1 - 1 × 1` | | | `1 × 1 - 1 × 2` | `3 × 1 - 1 × (-1)` | `3 × 2 - 1 × (-1)` | |
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= | | `2 -1` | `-1 -1` | `-1 -2` | | | `1 -1` | `3 -1` | `3 -1` | | | `1 -2` | `3 +1` | `6 +1` | |
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= | | `1` | `-2` | `-3` | | | `0` | `2` | `2` | | | `-1` | `4` | `7` | |
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2. Find `"Minor"(B)` ... `B=[[2,3,1],[0,5,6],[1,1,2]]`
Solution:
`MINOR(B)` | = | `MINOR` | | `2` | `3` | `1` | | | `0` | `5` | `6` | | | `1` | `1` | `2` | |
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= | | `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` | |
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= | | `10 -6` | `0 -6` | `0 -5` | | | `6 -1` | `4 -1` | `2 -3` | | | `18 -5` | `12 +0` | `10 +0` | |
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= | | `4` | `-6` | `-5` | | | `5` | `3` | `-1` | | | `13` | `12` | `10` | |
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This material is intended as a summary. Use your textbook for detail explanation. Any bug, improvement, feedback then
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