If the subspace of all solutions of Ax0 has a basis consisti

If the subspace of all solutions of Ax=0 has a basis consisting of four vectors and if A is a 4 times 6 matrix, what is the rank of A?

dimkerA=4
so by the rank-nullity theorem

rank(A)=number of columnsdimkerA

= 6-4
= 2

Answer :2

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http://math.stackexchange.com/questions/1117644/rank-of-a-matrix-from-a-5-x-7-matrix-with-a-basis-of-3-vectors