→ citynew :...........對!!我白癡!!!居然忘了乘反矩陣了!! 10/11 22:34
: 2. - - - -
: │1 0 1│ │a b c│
: A = │2 -1 2│ B=│d e f│
: │0 2 -1│ │g h i│
: - - - -
: 已知ABA = I3，求b+d+i=? (-13)
ABA = I_3
=>BA = A^(-1)
=>B = A^(-1)A^(-1)
| -3 2 1 |
A^(-1) = | 2 -1 0 |
| 4 -2 -1 |
| x -10 x |
B = | -8 x x |
| x x 5 | x:用不到就懶得算了XD
b+d+i=-13
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