Step-by-step explanation:
a = 2i + j - k
b = -1 -7j + k
a × b = (2i + j - k) (-1 + 7j + k)
-2i + 14ij + 2ik - j + 7j^2 + jk + k -7jk - k^2
-2i + 14ij + 2ik -j +7j^2 +jk - 7jk + k - k^2
-2i + 14ij + 2ik - j +7j^2 - 6jk + k - k^2
