3 added 97 characters in body edited Jul 21 '15 at 19:30 Szabolcs 172k1818 gold badges468468 silver badges10001000 bronze badges Update: it seems this only works in 10.1 and later, but not in 10.0. This works: Assuming[(a | b | c) ∈ Matrices[{d, d}], TensorExpand@Transpose[a.(b + c)]]  (* Transpose[b, {2, 1}].Transpose[a, {2, 1}] + Transpose[c, {2, 1}].Transpose[a, {2, 1}] *)  We needed to tell Mathematica that a, b and c are square matrices and use TensorExpand. Check here: Symbolic tensors. Update: it seems this only works in 10.1 and later, but not in 10.0. This works: Assuming[(a | b | c) ∈ Matrices[{d, d}], TensorExpand@Transpose[a.(b + c)]]  We needed to tell Mathematica that a, b and c are square matrices and use TensorExpand. Check here: Symbolic tensors. Update: it seems this only works in 10.1 and later, but not in 10.0. This works: Assuming[(a | b | c) ∈ Matrices[{d, d}], TensorExpand@Transpose[a.(b + c)]]  (* Transpose[b, {2, 1}].Transpose[a, {2, 1}] + Transpose[c, {2, 1}].Transpose[a, {2, 1}] *)  We needed to tell Mathematica that a, b and c are square matrices and use TensorExpand. Check here: Symbolic tensors. 2 added 76 characters in body edited Jul 21 '15 at 19:21 Szabolcs 172k1818 gold badges468468 silver badges10001000 bronze badges Update: it seems this only works in 10.1 and later, but not in 10.0. This works: Assuming[(a | b | c) ∈ Matrices[{d, d}], TensorExpand@Transpose[a.(b + c)]]  We needed to tell Mathematica that a, b and c are square matrices and use TensorExpand. Check here: Symbolic tensors. This works: Assuming[(a | b | c) ∈ Matrices[{d, d}], TensorExpand@Transpose[a.(b + c)]]  We needed to tell Mathematica that a, b and c are square matrices and use TensorExpand. Check here: Symbolic tensors. Update: it seems this only works in 10.1 and later, but not in 10.0. This works: Assuming[(a | b | c) ∈ Matrices[{d, d}], TensorExpand@Transpose[a.(b + c)]]  We needed to tell Mathematica that a, b and c are square matrices and use TensorExpand. Check here: Symbolic tensors. 1 answered Jul 21 '15 at 18:33 Szabolcs 172k1818 gold badges468468 silver badges10001000 bronze badges This works: Assuming[(a | b | c) ∈ Matrices[{d, d}], TensorExpand@Transpose[a.(b + c)]]  We needed to tell Mathematica that a, b and c are square matrices and use TensorExpand. Check here: Symbolic tensors.