| 1. |
Use the diagonals method.
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| 3. |
Expand along row 1.
 | | -1 | -19 | 8 | | -12 | 12 | 6 | | -9 | -17 | -14 |
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| 4. |
Expand along column 3.
 | | -1 | -19 | 17 | | 12 | 15 | -17 | | -7 | 13 | -9 |
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| 6. |
Use the diagonals method.
 | | -10 | -20 | 3 | | 11 | -2 | -19 | | 13 | -18 | 17 |
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| 8. |
Expand along column 1.
 | | 16 | 3 | -16 | | -20 | 2 | -5 | | 1 | -1 | -9 |
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| 9. |
Use the diagonals method.
 | | -14 | 19 | -20 | | 10 | -1 | 20 | | 4 | -9 | 6 |
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| 10. |
Expand along column 2.
 | | -15 | 18 | 2 | | 17 | 3 | -2 | | -13 | 9 | -16 |
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| 12. |
Use the diagonals method.
 | | -1 | -14 | 18 | | -17 | 6 | -19 | | 10 | 1 | -5 |
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| 13. |
Use the diagonals method.
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| 14. |
Expand along column 3.
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| 15. |
Use the diagonals method.
 | | 20 | -13 | -5 | | 3 | 18 | 12 | | -9 | 6 | 15 |
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| 18. |
Expand along row 3.
 | | -1 | -10 | -12 | | -6 | -16 | 1 | | 18 | 7 | -2 |
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| 20. |
Use the diagonals method.
 | | -10 | -5 | -11 | | -17 | 16 | 2 | | -15 | 12 | 11 |
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| 21. |
Expand along row 2.
 | | -18 | -9 | -12 | | 4 | 11 | -1 | | 5 | 13 | -8 |
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