Solution - Simplification or other simple results

Step  1  :

Trying to factor by splitting the middle term

 1.1     Factoring  x²+3x-504 

The first term is,  x²  its coefficient is  1 .
The middle term is,  +3x  its coefficient is  3 .
The last term, "the constant", is  -504 

Step-1 : Multiply the coefficient of the first term by the constant   1 • -504 = -504 

Step-2 : Find two factors of  -504  whose sum equals the coefficient of the middle term, which is   3 .

Step-3 : Rewrite the polynomial splitting the middle term using the two factors found in step 2 above,  -21  and  24 
                     x² - 21x + 24x - 504

Step-4 : Add up the first 2 terms, pulling out like factors :
                    x • (x-21)
              Add up the last 2 terms, pulling out common factors :
                    24 • (x-21)
Step-5 : Add up the four terms of step 4 :
                    (x+24)  •  (x-21)
             Which is the desired factorization

Final result :

  (x + 24) • (x - 21)