Linear algebra help: Subspaces

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SUMMARY

The discussion focuses on proving that the column space of the product of two matrices, C(AB), is a subset of the column space of the first matrix, C(A). The matrices A and B are defined with dimensions m x n and n x p respectively, leading to the product AB being m x p. The proof involves demonstrating that if a vector u is in C(AB), then there exists a vector v in R^n such that Av = u, confirming the subset relationship.

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Homework Statement


Prove that C(AB) is a subset of C(A) for matrices A,B, where C denotes column space.


Homework Equations


C(AB) = {b \in \mathbbcode{R}^m: Ax=b is consistent}


The Attempt at a Solution


I don't really know where to start.
 
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What's the definition of a subset?
 
to make things easier suppose that A is mxn, and B is nxp. so AB is mxp.

now..hint: suppose u is in C(AB), which means that ABx = u, for some x in Rp.

can you think of some vector v in Rn, with Av = u?

(what mapping do we know for sure produces a vector in Rn?)
 

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