Solving the System Ax = b: Is Full Rank Necessary?

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SUMMARY

The discussion centers on the linear algebra problem of solving the system Ax = b, where A is an m x n matrix with m > n. It is established that A must have full rank for a solution to exist, as a lack of full rank implies that b may not lie within the column space of A. A counterexample is suggested, using a simple matrix A composed of standard basis vectors in ℝm, demonstrating that if b is not in the range of A, then Ax = b has no solution.

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BobSea
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Homework Statement


The system Ax=b, with Amxn, and m>n, always has a solution when A has full rank. If False, give a counter example, if True, say why.



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The Attempt at a Solution


I want to say False because b doesn't need to be in the range of A, so Ax=b wouldn't have a solution. However, I'm having trouble making a counter example (i.e. A = 3x2 matrix and b = 3x1 matrix) that proves the point.
 
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Your reasoning is correct. For a counterexample, try a very simple A whose columns are elements of the standard basis for \mathbb{R}^m.
 

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