Answer
These matrices can't be equal.
Work Step by Step
Two matrices are equal if they have the same dimension and
if corresponding elements, position by position, are equal.
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$[ \ x\ y\ z\ ]$ is a 1$\times$3 matrix,
$[\ 21\ 6\ ]$ is a 1$\times$2 matrix.
They don't have the same dimension, so
these matrices can't be equal.
