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Let's do one:

| top row: 1 , 2 , 3  middle row: 4 , 5 , 6  bottom row: 7 , 8 , 9 |

| top row: 1 , 2, 3  middle row: 4 , 5 , 6  bottom row: 7 , 8, 9 | outside top row: 1 , 2  outside middle row: 4 , 5  outside bottom row: 7 , 8 ... multiply 1 , 5 , and 9 ... + ... multiply 2 , 6 , and 7 ... + ... multiply 3 , 4,  and 8 ... + 000-red-vertical-line.gif
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| top row: 1 , 2, 3  middle row: 4 , 5 , 6  bottom row: 7 , 8, 9 | outside top row: 1 , 2  outside middle row: 4 , 5  outside bottom row: 7 , 8 ... multiply 7 , 5 , and 3 ... - ... multiply 8 , 6 , and 1 ... - ... multiply 9 , 4, and 2 ... -


= ( 1 ) ( 5 ) ( 9 ) + ( 2 ) ( 6 ) ( 7 ) + ( 3 ) ( 4 ) ( 8 ) - ( 7 ) ( 5 ) ( 3 ) - ( 8 ) ( 6 ) ( 1 ) - ( 9 ) ( 4 ) ( 2 )
 

= 45 + 84 + 96 - 105 - 48 - 72 = 0