# Linear transformation - linear matrix & kernel

I have a problem understanding getting the KERNEL and IMAGE of a linear transformation. We have the following transformation given: $$\mathbb{R}_{2}[ x ] \rightarrow \mathbb{R}_{2}[ x ]$$ $$(\phi (p))(x) = (x p(x+1))' - 2p(x)$$

We first have to find its matrix in basis $$\{ 1, x, x^2 \}$$ which I know how to get. The transformation matrix result is:

$$\begin{bmatrix} -1& 1& 1\\ 0& 0& 4\\ 0& 0& 1 \end{bmatrix}$$

How do I get the KERNEL and the IMAGE from it ?

Would really appretiate an explanation, not just the result.

THANKS !

The image is generated by vectors that have the columns of the matrix as coordinates. Therefore the image is generated by $1$ and $1+4x+x^2$. These vectors are also linearly independent, so they form a basis.

The kernel is the set of vectors whose coordinates $X$ solve $MX=0$, where $M$ is the matrix.

Solving the system you get that the kernel is formed by vectors with coordinates $(a,a,0)$, thus a basis for the Kernel is the vector $1+x$.

• Aha thanks I got the image part, but I still don't understand how you get the kernel. Can you be more detailed please ? – box Jul 30 '14 at 12:53
• Which part you don't understand? – user126154 Jul 30 '14 at 12:56
• do you know the definition of kernel? – user126154 Jul 30 '14 at 12:57
• and what the matrix associated to a base does? – user126154 Jul 30 '14 at 12:57
• Solving the system part :). – box Jul 30 '14 at 12:57

To find the kernel just solve the homogeneous system

$$AX=0,\quad X = [x_1,x_2,x_3]^T.$$

The image is the space spanned by the column vectors of $A$.