2. is Nilpotent Matrix ?
`[[2,2,3],[1,2,3],[-1,-2,-3]]`
Solution:
A square matrix `A` is called a nilpotent matrix, if `A^m = 0` for some positive integer m.
`A` | = | | `2` | `2` | `3` | | | `1` | `2` | `3` | | | `-1` | `-2` | `-3` | |
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`A×A` | = | | `2` | `2` | `3` | | | `1` | `2` | `3` | | | `-1` | `-2` | `-3` | |
| × | | `2` | `2` | `3` | | | `1` | `2` | `3` | | | `-1` | `-2` | `-3` | |
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= | | `2×2+2×1+3×-1` | `2×2+2×2+3×-2` | `2×3+2×3+3×-3` | | | `1×2+2×1+3×-1` | `1×2+2×2+3×-2` | `1×3+2×3+3×-3` | | | `-1×2-2×1-3×-1` | `-1×2-2×2-3×-2` | `-1×3-2×3-3×-3` | |
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= | | `4+2-3` | `4+4-6` | `6+6-9` | | | `2+2-3` | `2+4-6` | `3+6-9` | | | `-2-2+3` | `-2-4+6` | `-3-6+9` | |
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= | | `3` | `2` | `3` | | | `1` | `0` | `0` | | | `-1` | `0` | `0` | |
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`(A^2)×A` | = | | `3` | `2` | `3` | | | `1` | `0` | `0` | | | `-1` | `0` | `0` | |
| × | | `2` | `2` | `3` | | | `1` | `2` | `3` | | | `-1` | `-2` | `-3` | |
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= | | `3×2+2×1+3×-1` | `3×2+2×2+3×-2` | `3×3+2×3+3×-3` | | | `1×2+0×1+0×-1` | `1×2+0×2+0×-2` | `1×3+0×3+0×-3` | | | `-1×2+0×1+0×-1` | `-1×2+0×2+0×-2` | `-1×3+0×3+0×-3` | |
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= | | `6+2-3` | `6+4-6` | `9+6-9` | | | `2+0+0` | `2+0+0` | `3+0+0` | | | `-2+0+0` | `-2+0+0` | `-3+0+0` | |
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= | | `5` | `4` | `6` | | | `2` | `2` | `3` | | | `-2` | `-2` | `-3` | |
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`(A^3)×A` | = | | `5` | `4` | `6` | | | `2` | `2` | `3` | | | `-2` | `-2` | `-3` | |
| × | | `2` | `2` | `3` | | | `1` | `2` | `3` | | | `-1` | `-2` | `-3` | |
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= | | `5×2+4×1+6×-1` | `5×2+4×2+6×-2` | `5×3+4×3+6×-3` | | | `2×2+2×1+3×-1` | `2×2+2×2+3×-2` | `2×3+2×3+3×-3` | | | `-2×2-2×1-3×-1` | `-2×2-2×2-3×-2` | `-2×3-2×3-3×-3` | |
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= | | `10+4-6` | `10+8-12` | `15+12-18` | | | `4+2-3` | `4+4-6` | `6+6-9` | | | `-4-2+3` | `-4-4+6` | `-6-6+9` | |
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= | | `8` | `6` | `9` | | | `3` | `2` | `3` | | | `-3` | `-2` | `-3` | |
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`(A^4)×A` | = | | `8` | `6` | `9` | | | `3` | `2` | `3` | | | `-3` | `-2` | `-3` | |
| × | | `2` | `2` | `3` | | | `1` | `2` | `3` | | | `-1` | `-2` | `-3` | |
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= | | `8×2+6×1+9×-1` | `8×2+6×2+9×-2` | `8×3+6×3+9×-3` | | | `3×2+2×1+3×-1` | `3×2+2×2+3×-2` | `3×3+2×3+3×-3` | | | `-3×2-2×1-3×-1` | `-3×2-2×2-3×-2` | `-3×3-2×3-3×-3` | |
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= | | `16+6-9` | `16+12-18` | `24+18-27` | | | `6+2-3` | `6+4-6` | `9+6-9` | | | `-6-2+3` | `-6-4+6` | `-9-6+9` | |
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= | | `13` | `10` | `15` | | | `5` | `4` | `6` | | | `-5` | `-4` | `-6` | |
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`(A^5)×A` | = | | `13` | `10` | `15` | | | `5` | `4` | `6` | | | `-5` | `-4` | `-6` | |
| × | | `2` | `2` | `3` | | | `1` | `2` | `3` | | | `-1` | `-2` | `-3` | |
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= | | `13×2+10×1+15×-1` | `13×2+10×2+15×-2` | `13×3+10×3+15×-3` | | | `5×2+4×1+6×-1` | `5×2+4×2+6×-2` | `5×3+4×3+6×-3` | | | `-5×2-4×1-6×-1` | `-5×2-4×2-6×-2` | `-5×3-4×3-6×-3` | |
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= | | `26+10-15` | `26+20-30` | `39+30-45` | | | `10+4-6` | `10+8-12` | `15+12-18` | | | `-10-4+6` | `-10-8+12` | `-15-12+18` | |
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= | | `21` | `16` | `24` | | | `8` | `6` | `9` | | | `-8` | `-6` | `-9` | |
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`(A^6)×A` | = | | `21` | `16` | `24` | | | `8` | `6` | `9` | | | `-8` | `-6` | `-9` | |
| × | | `2` | `2` | `3` | | | `1` | `2` | `3` | | | `-1` | `-2` | `-3` | |
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= | | `21×2+16×1+24×-1` | `21×2+16×2+24×-2` | `21×3+16×3+24×-3` | | | `8×2+6×1+9×-1` | `8×2+6×2+9×-2` | `8×3+6×3+9×-3` | | | `-8×2-6×1-9×-1` | `-8×2-6×2-9×-2` | `-8×3-6×3-9×-3` | |
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= | | `42+16-24` | `42+32-48` | `63+48-72` | | | `16+6-9` | `16+12-18` | `24+18-27` | | | `-16-6+9` | `-16-12+18` | `-24-18+27` | |
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= | | `34` | `26` | `39` | | | `13` | `10` | `15` | | | `-13` | `-10` | `-15` | |
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`(A^7)×A` | = | | `34` | `26` | `39` | | | `13` | `10` | `15` | | | `-13` | `-10` | `-15` | |
| × | | `2` | `2` | `3` | | | `1` | `2` | `3` | | | `-1` | `-2` | `-3` | |
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= | | `34×2+26×1+39×-1` | `34×2+26×2+39×-2` | `34×3+26×3+39×-3` | | | `13×2+10×1+15×-1` | `13×2+10×2+15×-2` | `13×3+10×3+15×-3` | | | `-13×2-10×1-15×-1` | `-13×2-10×2-15×-2` | `-13×3-10×3-15×-3` | |
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= | | `68+26-39` | `68+52-78` | `102+78-117` | | | `26+10-15` | `26+20-30` | `39+30-45` | | | `-26-10+15` | `-26-20+30` | `-39-30+45` | |
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= | | `55` | `42` | `63` | | | `21` | `16` | `24` | | | `-21` | `-16` | `-24` | |
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`(A^8)×A` | = | | `55` | `42` | `63` | | | `21` | `16` | `24` | | | `-21` | `-16` | `-24` | |
| × | | `2` | `2` | `3` | | | `1` | `2` | `3` | | | `-1` | `-2` | `-3` | |
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= | | `55×2+42×1+63×-1` | `55×2+42×2+63×-2` | `55×3+42×3+63×-3` | | | `21×2+16×1+24×-1` | `21×2+16×2+24×-2` | `21×3+16×3+24×-3` | | | `-21×2-16×1-24×-1` | `-21×2-16×2-24×-2` | `-21×3-16×3-24×-3` | |
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= | | `110+42-63` | `110+84-126` | `165+126-189` | | | `42+16-24` | `42+32-48` | `63+48-72` | | | `-42-16+24` | `-42-32+48` | `-63-48+72` | |
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= | | `89` | `68` | `102` | | | `34` | `26` | `39` | | | `-34` | `-26` | `-39` | |
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`A` is not a nilpotent matrix
This material is intended as a summary. Use your textbook for detail explanation.
Any bug, improvement, feedback then