# Direct sum of nullspace and range

1. Sep 10, 2013

### Bipolarity

Is this true? I am studying direct sums and was wondering if the following statement holds? It seems to be true if one considers the proof of the dimension theorem, but I need to be sure, so I can steer my proof toward a particular direction.

$N(T) \bigoplus R(T) = V$ where $V$ is the source of the linear map $T:V → V$ ?

BiP

2. Sep 10, 2013

### Office_Shredder

Staff Emeritus
It's not. The null space and range have dimensions which add up to the dimension of V, but they can overlap. For example consider the map

T(x,y) = (y,0).

This is a linear map from R2 to R2. The null space is (x,0) for x in R and the range is (x,0) for x in R, so N(T)+R(T) is just the x-axis

3. Sep 10, 2013

### Bipolarity

I see. Suppose that you knew the statement to be true. Then could you conclude that T is invertible?

BiP

4. Sep 10, 2013

### Office_Shredder

Staff Emeritus
It's not hard to construct a projection in two dimensions which is a counterexample to that claim