Hint for the Charpoly exercise

First of all, what is this exercise about? The idea is that you find yourself writing a document which contains lots of characteristic polynomials of 2 by 2 matrices, such as

ê ê ê 2-l -1 3 1-l ê ê ê ,       ê ê ê 4-l 0 2 -3-l ê ê ê ,      and       ê ê ê 10-x 3 -4 2-x ê ê ê .

These take quite a lot of time to format in L^AT_EX, so you'd like just to write 
\Charpoly{2}{-1}{3}{1}{\lambda} 
\Charpoly{4}{0}{2}{-3}{\lambda}, and  
\Charpoly{10}{3}{-4}{2}{x}
to produce them quickly.

If you find this exercise difficult, follow these steps:

1. Write the L^AT_EX code necessary to produce
   

   ê ê ê

   2-l -1 3 1-l

   ê ê ê

   
   .

   
   

2. Turn this into a command, i.e. 
   \newcommand{\Charpoly}{your L^AT_EX code}
3. Now replace this command with 
   \newcommand{\Charpoly}[5]{your L^AT_EX code}
   and, in the L^AT_EX code, replace the particular numbers and the l for this example with appropriate #1, #2, etc.