Linear algebra introduction read

{{1.5, 1.6}, {1.7, 1.8}}

{{1.5, 1.6}, {1.7, 1.8}}

Table[1 / (i * j), {i, 3}, {j, 3}]

{{1, 1/2, 1/3}, {1/2, 1/4, 1/6}, {1/3, 1/6, 1/9}}

mat = Table[Subscript[m, i, j], {i, 3}, {j, 3}]

{{Subscript[m, 1, 1], Subscript[m, 1, 2], Subscript[m, 1, 3]}, {Subscript[m, 2, 1], Subscript[m, 2, 2], Subscript[m, 2, 3]}, {Subscript[m, 3, 1], Subscript[m, 3, 2], Subscript[m, 3, 3]}}

Dimensions[mat]

{3, 3}

MatrixQ[ mat]

True

MatrixForm[mat]

MatrixForm[{{Subscript[m, 1, 1], Subscript[m, 1, 2], Subscript[m, 1, 3]}, {Subscript[m, 2, 1], Subscript[m, 2, 2], Subscript[m, 2, 3]}, {Subscript[m, 3, 1], Subscript[m, 3, 2], Subscript[m, 3, 3]}}]

mat = {{1.5, 1.6}, {1.7, 1.8}};
eqns = Thread[mat.{x, y} == {2, 6}]

{1.5*x + 1.6*y == 2, 1.7*x + 1.8*y == 6}

Solve[eqns, {x, y}]

{{x -> 299.9999999999998, y -> -279.9999999999997}}

LinearSolve[mat, {2, 6}]

{299.99999999999807, -279.9999999999982}