Solution - Factoring multivariable polynomials

Reformatting the input :

Changes made to your input should not affect the solution:

 (1): "r2"   was replaced by   "r^2". 

Step  1  :

Trying to factor a multi variable polynomial :

 1.1    Factoring    r² - 2rx - 80x 

Try to factor this multi-variable trinomial using trial and error 

 Factorization fails

Final result :

  r2 - 2rx - 80x