第三题
a = {{1, 2, 3, 4, 5}, {6, 7, 8, 9, 10}, {11, 12, 13, 14, 15}, {16, 17,
18, 19, 20}, {21, 22, 23, 24, 25}};
b = {{3, 0, 16}, {17, -6, 9}, {0, 23, -4}, {9, 7, 0}, {4, 13, 11}};
c = a.b;(*两个矩阵的乘积*)
c // MatrixForm
c[[2 ;;]][[All, {2, 3}]] // MatrixForm(*右下角4*2的小矩阵*)
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