# Math Help - Finding the Characteristic Polynomial of a Map

1. ## Finding the Characteristic Polynomial of a Map

Let $A: V \rightarrow V$ be a linear map satisfying the property $A^2 = A$. Assume that $dim V = n, rank A = k.$ Find the characteristic polynomial of $A.$

I don't really know where to start, is this an application of the Cayley-Hamilton Theorem or something?

Thanks!

2. Originally Posted by h2osprey
Let $A: V \rightarrow V$ be a linear map satisfying the property $A^2 = A$. Assume that $dim V = n, rank A = k.$ Find the characteristic polynomial of $A.$

I don't really know where to start, is this an application of the Cayley-Hamilton Theorem or something?
Hint: The image of A is the eigenspace for the eigenvalue 1 (and has dimension k). The null space of A is the eigenspace for the eigenvalue 0 (and has dimension n–k).

3. Of course, it's all clear now. Thanks!