# Thread: column space, null space

1. ## column space, null space

Here are my problems:

Prove that if C is am mxn matrix over the field R of reals then R^n-Col(C^T) (direct sum) N(C), where Col (A) denotes the column space of the matrix A and N(A) denotes the right null space of A.

Plese, help!

2. Originally Posted by mivanova
Prove that if C is am mxn matrix over the field R of reals then R^n-Col(C^T) (direct sum) N(C), where Col (A) denotes the column space of the matrix A and N(A) denotes the right null space of A.
Note sure what the question is asking? Is that that this expression is zero?
If thus, I think you need to use the rank nullity theorem.
Define $T(\bold{x}) = A\bold{x}$ as a linear transformation $A: \mathbb{R}^n \to \mathbb{R}^m$.
But $\text{rank}(A)$ is the dimension of the column space.
And $\text{nullity}(A)$ is the dimension of the null space.
Thus the dimensions add up to $n$, the dimension of $\mathbb{R}^n$.

3. ## column space, null space

Hi,
Thank you so much for your answer. I don't think that this expressiin is zero. The way that is giving to us is to prove that R^n=Col(C^T)(dir sum)N(C).
And, sorry if it is a stupid questions, but what differrence will it make if it is "right" null space or "left"?

Thank you so much!