To create a matrix, Press [MTRW] to access Matrix Writer Type numbers or letters and press [ENTER] for each number or letter typed. 
The HP49 Matrix Writer 
Alphanumerical Elements HP49 supports symbolic elements and you can type them directly in the Matrix Writer, like a number. You just need keep the alpha key actived. 
Typing Alphanumerical Elements 


Lets invert the matrix 1 write the matrix 2Press [ ENTER ] 3 You will see 
4 Press 1/X and [ ENTER ] to write INV ( ANS ( 1 ) ) 5It will show 6press [ ENTER ] to see result: 